Problem:
 Score : 400 points    Problem Statement In this problem, we only consider strings consisting of lowercase English letters.  Strings s and t are said to be isomorphic when the following conditions are satisfied:   |s| = |t| holds.  For every pair i, j , one of the following holds:  s_i = s_j and t_i = t_j .  s_i \neq s_j and t_i \neq t_j .     For example, abcac and zyxzx are isomorphic, while abcac and ppppp are not.  A string s is said to be in normal form when the following condition is satisfied:   For every string t that is isomorphic to s , s \leq t holds. Here \leq denotes lexicographic comparison.   For example, abcac is in normal form, but zyxzx is not since it is isomorphic to abcac , which is lexicographically smaller than zyxzx .  You are given an integer N .
Print all strings of length N that are in normal form, in lexicographically ascending order.      Constraints  1 \leq N \leq 10  All values in input are integers.         Input Input is given from Standard Input in the following format:  N       Output Assume that there are K strings of length N that are in normal form: w_1, \ldots, w_K in lexicographical order.
Output should be in the following format:  w_1  :  w_K         Sample Input 1 1      Sample Output 1 a       Sample Input 2 2      Sample Output 2 aa
ab

Solution (Python):
def main(sample_file = ''):

    """ convenient functions
    
    
    
    
    
    """

    """convenient decorator
    
    
        
        
        
        
        
        
        
        
        
        
    """
    
    
    import sys
    sys.setrecursionlimit(10**7)
    from itertools import accumulate, combinations, permutations, product 
    
    from math import factorial, ceil, floor, sqrt
    def factorize(n):
        """return the factors of the Arg and count of each factor
        
        Args:
            n (long): number to be resolved into factors
        
        Returns:
            list of tuples: factorize(220) returns [(2, 2), (5, 1), (11, 1)]
        """
        fct = []  
        b, e = 2, 0  
        while b * b <= n:
            while n % b == 0:
                n = n // b
                e = e + 1
            if e > 0:
                fct.append((b, e))
            b, e = b + 1, 0
        if n > 1:
            fct.append((n, 1))
        return fct
    def combinations_count(n, r):   
        """Return the number of selecting r pieces of items from n kinds of items.
        
        Args:
            n (long): number
            r (long): number
        
        Raises:
            Exception: not defined when n or r is negative
        
        Returns:
            long: number
        """
        
        if n < 0 or r < 0:
            raise Exception('combinations_count(n, r) not defined when n or r is negative')
        if n - r < r: r = n - r
        if r < 0: return 0
        if r == 0: return 1
        if r == 1: return n
        numerator = [n - r + k + 1 for k in range(r)]
        denominator = [k + 1 for k in range(r)]
        for p in range(2,r+1):
            pivot = denominator[p - 1]
            if pivot > 1:
                offset = (n - r) % p
                for k in range(p-1,r,p):
                    numerator[k - offset] /= pivot
                    denominator[k] /= pivot
        result = 1
        for k in range(r):
            if numerator[k] > 1:
                result *= int(numerator[k])
        return result
    def combinations_with_replacement_count(n, r):
        """Return the number of selecting r pieces of items from n kinds of items allowing individual elements to be repeated more than once.
        
        Args:
            n (long): number
            r (long): number
        
        Raises:
            Exception: not defined when n or r is negative
        
        Returns:
            long: number
        """
        if n < 0 or r < 0:
            raise Exception('combinations_with_replacement_count(n, r) not defined when n or r is negative')
        elif n == 0:
            return 1
        else:
            return combinations_count(n + r - 1, r)
    from bisect import bisect_left, bisect_right
    from collections import deque, Counter, defaultdict 
    from heapq import heapify, heappop, heappush, heappushpop, heapreplace,nlargest,nsmallest 
    from copy import deepcopy, copy 
    import operator
    from operator import itemgetter 
    
    
    from functools import reduce, lru_cache
    def chmin(x, y):
        """change minimum
        if x > y, x = y and return (x, True).
        convenient when solving problems of dp[i]
        
        Args:
            x (long): current minimum value
            y (long): potential minimum value
        
        Returns:
            (x, bool): (x, True) when updated, else (x, False)
        """
        if x > y:
            x = y
            return (x, True)
        else:
            return (x, False)
    def chmax(x, y):
        """change maximum
        if x < y, x = y and return (x, True).
        convenient when solving problems of dp[i]
        
        Args:
            x (long): current maximum value
            y (long): potential maximum value
        
        Returns:
            (x, bool): (x, True) when updated, else (x, False)
        """
        if x < y:
            x = y
            return (x, True)
        else:
            return (x, False)

    from fractions import gcd 
    def gcds(numbers):
        return reduce(gcd, numbers)
    def lcm(x, y):
        return (x * y) // gcd(x, y)
    def lcms(numbers):
        return reduce(lcm, numbers, 1)
    def make_divisors(n, reversed=False):
        """create list of divisors
        
        Args:
            number (int): number from which list of divisors is created
            reversed (bool, optional): ascending order if False. Defaults to False.
        
        Returns:
            list: list of divisors
        """
        divisors = set()
        for i in range(1, int(n**0.5)+1):
            if n % i == 0:
                divisors.add(i)
                divisors.add(n//i)
        return sorted(list(divisors),reverse=reversed)
    
    
    
    INF = 10 ** 18
    MOD = 10 ** 9 + 7
    modpow = lambda a, n, p = MOD: pow(a, n, p) 
    def modinv(a, p = MOD):
        
        
        return modpow(a, p-2, p)
    def modinv_list(n, p = MOD):
        if n <= 1:
            return [0,1][:n+1]
        else:
            inv_t = [0,1]
            for i in range(2, n+1):
                inv_t += [inv_t[p % i] * (p - int(p / i)) % p]
            return inv_t
    def modfactorial_list(n, p = MOD):
        if n == 0:
            return [1]
        else:
            l = [0] * (n+1)
            tmp = 1
            for i in range(1, n+1):
                tmp = tmp * i % p
                l[i] = tmp
            return l
    def modcomb(n, k, fac_list = [], p = MOD):
        
        
        from math import factorial
        if n < 0 or k < 0 or n < k: return 0
        if n == 0 or k == 0: return 1
        if len(fac_list) <= n:
            a = factorial(n) % p
            b = factorial(k) % p
            c = factorial(n-k) % p
        else:
            a = fac_list[n]
            b = fac_list[k]
            c = fac_list[n-k]
        return (a * modpow(b, p-2, p) * modpow(c, p-2, p)) % p
    def modadd(a, b, p = MOD):
        return (a + b) % MOD
    def modsub(a, b, p = MOD):
        return (a - b) % p
    def modmul(a, b, p = MOD):
        return ((a % p) * (b % p)) % p
    def moddiv(a, b, p = MOD):
        return modmul(a, modpow(b, p-2, p))

    class UnionFindTree:
        """union find tree class
        TODO: fix this description...
        how to use (example):
        >>  uf = UnionFindTree(N) 
        >>  if uf.find_root(a) == uf.find_root(b):
        >>      do something
        >>  else:
        >>      do something
        >>      uf.unite(a, b)
        """
        def __init__(self, N):
            self.root = [-1] * (N+1)
            self.rank   = [0]  * (N+1)
            self.connected_num = [1] * (N+1)
    
        def find_root(self,x):
            root = self.root
            while root[x] != -1:
                x = root[x]
            return x
    
        def unite(self,x,y):
            root = self.root
            rank = self.rank
            connected_num = self.connected_num
            find_root = self.find_root
    
            rx = find_root(x)
            ry = find_root(y)
            if rx != ry:
                if rank[rx] < rank[ry]:
                    root[rx] = ry
                    rx,ry = ry,rx
                else:
                    if rank[rx] == rank[ry]:
                        rank[rx] += 1
                    root[ry] = rx       
                connected_num[rx] += connected_num[ry]

    
    
    
    
    

    def BellmanFord(N, M, ABC, vertex_start, vertex_end, value_if_inf = -1, find_shortest = False):
        """to calculate furthest or shortest length between vertex_start and vertex_end using BellmanFord algorithm
        
        Args:
            N (int): number of vertices
            M (int): number of edges
            ABC (list): [(ai, bi, ci) for _ in range(N)] where i-th edge is directed from vertex ai to vertex bi and the length is ci 
            vertex_start (int): start vertex. usually use 0.
            vertex_end (int): end vertex. usually use N-1.
            value_if_inf (int or string as you like, optional): value you want when the furthest (or shortest) distance is infinite (or -infinite). Defaults to -1.
            find_shortest (bool, optional): choose False to find furthest path. Defaults to False.
        
        Returns:
            int or string: normally int (but can be str if you set value_if_inf to str)
            
        Example:
                N, M, P = R()
                ABC = [R() for _ in range(M)]
                ABC = [(a-1, b-1, c-P) for a, b, c in ABC]
                print(BellmanFord(N, M, ABC, 0, N-1, value_if_inf = 'inf'))

        """

        def make_reachable_list(N, M, ABC, vertex_start, vertex_end):
            reachable_to_direct = defaultdict(list)
            reachable_from_direct = defaultdict(list)
            reachable_from_start = [False] * N
            reachable_to_end = [False] * N
            reachable_from_start[vertex_start] = True
            reachable_to_end[vertex_end] = True
            reachable_from_both_sides = [False] * N
            dfs_from_start = []
            dfs_to_end = []
            for a, b, c in ABC:
                reachable_to_direct[a].append(b)
                reachable_from_direct[b].append(a)
                if a == vertex_start:
                    dfs_from_start.append(b)
                    reachable_from_start[b] = True
                if b == vertex_end:
                    dfs_to_end.append(a)
                    reachable_to_end[a] = True
            while dfs_from_start:
                v = dfs_from_start.pop()
                for i in reachable_to_direct[v]:
                    if not reachable_from_start[i]:
                        reachable_from_start[i] = True
                        dfs_from_start.append(i)
            while dfs_to_end:
                v = dfs_to_end.pop()
                for i in reachable_from_direct[v]:
                    if not reachable_to_end[i]:
                        reachable_to_end[i] = True
                        dfs_to_end.append(i)
            for i in range(N):
                reachable_from_both_sides[i] = reachable_from_start[i] and reachable_to_end[i]
            return reachable_from_both_sides
        
        reachable_from_both_sides = make_reachable_list(N, M, ABC, vertex_start, vertex_end)
        
        if find_shortest:
            dist = [INF for i in range(N)]
        else:
            dist = [-INF for i in range(N)]
        
        dist[vertex_start] = 0
        for i in range(N):
            updated = False
            for a, b, c in ABC:
                if not reachable_from_both_sides[a]:
                    continue
                elif find_shortest:
                    update_condition = dist[a] + c < dist[b]
                else:
                    update_condition = dist[a] + c > dist[b]
                if dist[a] != INF and update_condition:
                    dist[b] = dist[a] + c
                    updated = True
                    if i == N-1:
                        return value_if_inf
            if not updated:
                break
        return dist[vertex_end]

    """ initialize variables and set inputs
    
        
        
            
            
    
        
        
        
        
        
        
        
    
        
        
        
        
    
        
        
    """

    
    r = lambda: sys.stdin.readline().strip()
    r_int = lambda: int(r())
    r_float = lambda: float(r())
    R = lambda: list(map(int, r().split()))
    R_str = lambda: r().split()
    R_map = lambda: map(int, r().split())
    R_float = lambda: list(map(float, r().split()))
    R_tuple = lambda: tuple(map(int, r().split()))

    """ how to treat input
    
    
    
    
    
    
    
    """

    
    if sample_file:
        sys.stdin = open(sample_file)
        
    
    
    
    N = r_int()
    task = [('a', 1)]
    abc = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j']
    while task:
        s, l = task.pop()
        if len(s) == N:
            print(s)
        else:
            for i in range(l, -1, -1):
                u = ''.join((s, abc[i]))
                if i == l:
                    task.append((u, l+1))
                else:
                    task.append((u, l))
    
    
    
    

    """memo: how to use defaultdict of list
    
    Dic = defaultdict(list)
    
    Dic[x].append(y)
    
    for k, v in Dic.items():
    """
    
    """memo: how to solve binary problems
    
    >>> a = 5
    >>> bin_str_a = format(a, '
    >>> print(bin_str_a)
    0b0101 
    """
    
    """memo: how to solve the problem
    creating simple test/answer
    greed
    simple dp
    graph
    """

if __name__ == '__main__':
    main()

Solution (Python):
N = int(input())
def dfs(s):
  if len(s) == N:
    print(s)
    return
  else:
    for i in range(ord("a"), ord("z")+1):
      if i < ord(max(list(s)))+2:
        dfs(s+chr(i))
      else:
        return
dfs("a")

Solution (Python):
N = int(input())
def dfs(s):
  if len(s) == N:
    print(s)
    return
  else:
    for i in range(ord("a"), ord("z")+1):
      if max(list(s)) != chr(i-2):
        dfs(s+chr(i))
      else:
        return
dfs("a")

Solution (Python):
import sys 
sys.setrecursionlimit(4100000)

N = int(input())

def dfs(i,s):
    if len(s) == N:
        
        return print(s)
    
    for x in range(97,i + 1):
        t = s + chr(x)
        
        dfs(max(x + 1,i),t)
    
    
dfs(ord("a"),"")

Solution (Python):
N = int(input())

dp = [[] for _ in range(N)]
dp[0].append('a')

for i in range(1, N):
    for strings in dp[i-1]:
        j = 97
        while j <= ord(max(strings))+1:
            nextstr = strings
            nextstr += chr(j)
            dp[i].append(nextstr)
            j += 1

dp[N-1].sort()

for strings in dp[N-1]:
    print(strings)

Solution (Python):
def write(r):
    b=[chr(x+97) for x in r]
    print("".join(b))


def add(a,j):
    for c in a[j]:
        for d in range(max(c)+2):
            e=c+[d]
            a[j+1].append(e)
    

n=int(input())
a=[[] for x in range(n)]
a[0]=[[0]]
for j in range(n-1):
    add(a,j)
for r in a[n-1]:
    write(r)

Solution (Python):
s = input().split()
n = int(s[0])

st = ['a','b','c','d','e','f','g','h','i','j','k']


inis = [1,1,1,1,1,1,1,1,1,1,1]

def print_str( arry , num):
   str_a = ''
   for i in range(num):
     
     str_a = str_a + st[arry[i]-1]
   print(str_a)


def do_number_n( len ):
   global inis
   tsti = 0
   k = len - 1    
   print_str( inis , len)
   while True:
      inis[k] += 1
      for j in range(k,0,-1):
         
         if ( max(inis[0:j]) + 2 ) <= inis[j]  :
         
            inis[j-1] += 1
            inis[j] = 1
         
            
      
      if inis[0] > 1 :
         return        
      print_str( inis , len)
  
def main():
  do_number_n(n)
    
main()

Solution (Python):
n = int(input())
a = list(chr(i*97) for i in range(10))
ans = 'a'

def dfs():
    global ans, n
    if len(ans) == n:
        print(ans)
    else:
        max1 = 'a'
        for i in range(len(ans)):
            max1 = max(max1, ans[i])
        for i in range(ord(max1) - 95):
            ans += chr(i+97)
            dfs()
            ans = ans[:-1]

dfs()

Solution (Python):
N = int(input())
from collections import deque

def func(S):
  q = deque([S])
  while q:
    x = q.popleft()
    if len(x) == N:
      print(x)
    else:
      for char_no in range(ord('a'), max([ ord(i) for i in x ])+2):
        y = x + chr(char_no)
        q.append(y)


start = 'a'
func(start)

Solution (Python):
N=int(input())

def dfs(s, mx):
    if len(s) == N:
        print(s)
    else:
        for o in range(ord('a'),ord(mx)+1):
            dfs(s + chr(o), chr(ord(mx)+1) if o==ord(mx) else mx)


dfs("",'a')

Solution (Python):
import string
N=int(input())
A=string.ascii_letters
ans=["a"]*N
Ans=[1]*N

def search(n):
    if n!=N-1:
        for i in range(max(Ans)+1):
            Ans[n]=i+1
            ans[n]=A[i]
            search(n+1)
            Ans[n+1:]=[1]*(N-n-1)
    else:
        for i in range(max(Ans)+1):
            Ans[n]=i+1
            ans[n]=A[i]
            print("".join(ans))

if N==1:
    print("a")
else:
    search(1)

Solution (Python):
import string
N=int(input())
A=string.ascii_letters
ans=["a"]*N
Ans=[1]*N

def search(n):
    if n!=N-1:
        for i in range(max(Ans)+1):
            Ans[n]=i+1
            ans[n]=A[i]
            search(n+1)
            Ans[n+1:]=[1]*(N-n-1)
    else:
        for i in range(max(Ans)+1):
            Ans[n]=i+1
            ans[n]=A[i]
            print("".join(ans))

if N==1:
    print("a")
else:
    search(1)

Solution (Python):
N = int(input())

alphabet = [chr(97+i) for i in range(min(N,26))]


dp = [[None]*N for _ in range(N)]
dp[0][0] = [alphabet[0]]
for i in range(1,N):
	dp[0][i] = []



for n in range(1,N):
	for k in range(N):
		
		dp[n][k] = []
		for s in dp[n-1][k]:
			
			dp[n][k] += [s + alphabet[i] for i in range(k+1)]
		for s in dp[n-1][k-1]:
			dp[n][k] += [s + alphabet[k]]


ans = []
for k in range(N):
	ans += dp[N-1][k]
ans = sorted(ans)

for s in ans:
	if len(s)!=0:
		print(s)

Solution (Python):
def solve():
    N = int(input())
    
    codepoint = ord("a")
 
    
    i = 1
    
    ans = [["a", 1]]
    
    while i < N:
        
        tmp = []
        
        for w, j in ans:
            
            for k in range(j+1):
                if k != j:
                    tmp.append([w + chr(codepoint+k), j])
                
                else:
                    tmp.append([w + chr(codepoint+k), j+1])
        ans = tmp
        i += 1
 
    [print(a[0]) for a in ans]
 
    
if __name__ == "__main__":
    solve()

Solution (Python):
string=['a','b','c','d','e','f','g','h','i','j']
N=int(input())
res=[]
def dfs(ss):
  if len(ss)==N:
    ss=''.join(ss)
    res.append(ss)
  else:
    for i in range(string.index(max(ss))+2):
      a=ss+[string[i]]
      dfs(a)
  return res
ans=dfs(['a'])
for i in range(len(ans)):
  print(ans[i])

Solution (Python):
import math


def div_with_mod(x, y, mod):
    
    return x*pow(y, mod - 2, mod)


def comb(n, r, mod):
    
    nc = n
    for rc in range(1, r):
        nc -= 1
        n = n*nc % mod
        r = r*rc % mod

    return div_with_mod(n, r, mod)


def solve():
    N = int(input())
    
    codepoint = ord("a")

    def dfs(word, dep):
        if len(word) == N:
            return print(word)

        for i in range(dep):
            dfs(word + chr(codepoint+i), dep)

        dfs(word + chr(codepoint+dep), dep+1)

    dfs("a", 1)



if __name__ == "__main__":
    solve()

Solution (Python):
import sys

input = sys.stdin.readline


N = int(input())


def dfs(s, mx):
    if len(s) == N:
        print(s)
        return
    for c in range(ord("a"), mx + 2):
        t = s
        t += chr(c)
        dfs(t, max(c, mx))


dfs("", ord("a") - 1)

Solution (Python):
N = int(input())
s = 'abcdefghijklmn'


def f(d, now, kind):
    if d == N:
        print(now)
        return
    for i in range(kind):
        f(d + 1, now + s[i], kind)
    f(d + 1, now + s[kind], kind + 1)

f(0, '', 0)

Solution (Python):
import sys
sys.setrecursionlimit(500000)

N = int(input())
global ans
ans = []
def dfs(now,rank,root_,m):
    root = root_[:]
    if rank == N:
        root.append(now)
        ans.append(''.join([chr(i+ord('a')) for i in root]))
    else:
        root.append(now)
        for i in range(m+2):
            dfs(i,rank+1,root,max(m,i))

dfs(0,1,[],0)
ans.sort()
print(*ans,sep='\n')

Solution (Python):
import math


def div_with_mod(x, y, mod):
    
    return x*pow(y, mod - 2, mod)


def comb(n, r, mod):
    
    nc = n
    for rc in range(1, r):
        nc -= 1
        n = n*nc % mod
        r = r*rc % mod

    return div_with_mod(n, r, mod)


def solve():
    N = int(input())
    
    codepoint = ord("a")

    
    i = 1
    
    ans = [["a", 1]]
    
    while i < N:
        
        tmp = []
        
        for w, j in ans:
            
            for k in range(j+1):
                if k != j:
                    tmp.append([w + chr(codepoint+k), j])
                
                else:
                    tmp.append([w + chr(codepoint+k), j+1])
        ans = tmp
        i += 1

    [print(a[0]) for a in ans]

    
if __name__ == "__main__":
    solve()

Solution (Python):
def getStr(vars):
    if len(vars)==N:
        print(getPrintStr(vars))
        return
    
    vars.append(0)
    for i in range(0,max(vars)+2):
        vars[-1] = i
        
        getStr(vars)
    del vars[-1]
    return

def getPrintStr(vars):
    ret = ""
    for i in range(len(vars)):
        ret += "abcdefghijkl"[vars[i]]
    return ret

N = int(input())
 
getStr([0])

Solution (Python):
import sys
input = sys.stdin.readline
from operator import itemgetter
sys.setrecursionlimit(10000000)
INF = 10**30

S = "abcdefghijkl"
N = 0
def rec(s):
    if len(s) == N:
        print(''.join(s))
        return
    for i in range(len(set(s))+1):
        s.append(S[i])
        rec(s)
        s.pop()
    

def main():
    global N
    N = int(input().strip())
    rec([])

if __name__ == '__main__':
    main()

Solution (Python):
N = int(input())

def f(s, mx):
    if len(s) == N:
        print(s)
        return
    for i in range(mx+1):
        f(s + chr(ord("a") + i), max(mx, i+1))

f("", 0)

Solution (Python):
n = int(input())
dic = {0:'a',1:'b',2:'c',3:'d',4:'e',5:'f',6:'g',7:'h',8:'i',9:'j'}
ans = [["a",1]]
for i in range(1,n):
    tmp=[]
    for prev,val in ans:
        for j in range(val+1):
            tmp.append([prev+dic[j],val]) if j!=val else tmp.append([prev+dic[j],val+1])
    ans=tmp
ans=sorted(ans,key=lambda x:x[0])
for i in range(len(ans)):
    print(ans[i][0])

Solution (Python):
N=int(input())
dic={0:'a',1:'b',2:'c',3:'d',4:'e',5:'f',6:'g',7:'h',8:'i',9:'j'}
ans=[["a",1]]
for i in range(1,N):
    tmp=[]
    for prev,val in ans:
        for j in range(val+1):
            if j!=val:
                tmp.append([prev+dic[j],val])
            else:
                tmp.append([prev+dic[j],val+1])
    ans=tmp
ans=sorted(ans,key=lambda x:x[0])
for i in range(len(ans)):
    print(ans[i][0])

Solution (Python):
def standard_form(N):
    
    if N == 1:
        return ["a"]
    ans = []
    std_forms = standard_form(N - 1)
    max_char_idx = 2

    for std_form in std_forms:
        max_char_idx = max([ord(ch) for ch in std_form])

        for i in range(ord('a'), max_char_idx + 2):
            append_char = chr(i)
            ans.append(std_form + append_char)

    return ans


if __name__ == '__main__':
    N = int(input())
    ans = standard_form(N)
    ans.sort()
    for a in ans:
        print(a)

Solution (Python):
import math


def div_with_mod(x, y, mod):
    
    return x*pow(y, mod - 2, mod)


def comb(n, r, mod):
    
    nc = n
    for rc in range(1, r):
        nc -= 1
        n = n*nc % mod
        r = r*rc % mod

    return div_with_mod(n, r, mod)


def solve():
    N = int(input())
    list = [chr(ord("a")+i) for i in range(10)]

    def dfs(w, i):
        if len(w) == N:
            return print(w)

        for j in range(i):
            dfs(w+list[j], i)

        dfs(w + list[i], i + 1)

    dfs("", 0)



if __name__ == "__main__":
    solve()

Solution (Python):
alp='abcdefghijklmnopqrstuvwxyz'

def f(N, s, x):
  if len(s)==N:
    print(s)
    return
  for i in range(x+2):
    f(N, s+alp[i], max(x, i))
    
f(int(input()), 'a', 0)

Solution (Python):
def dfs(N, s, maxc):
    if len(s) == N:
        print(s)
    else:
        for i in range(ord(maxc)-ord('a') + 2):
            ord_c = ord('a')+i
            dfs(N, s+chr(ord_c), chr(max(ord_c, ord(maxc))))

N = int(input())
dfs(N, 'a', 'a')

Solution (Python):
import string

n = int(input())
s = string.ascii_letters[:n]

ans_list = ['a']
for i in range(n-1):
    ans_list = [ans + c for ans in ans_list for c in s[:len(set(ans)) + 1]]

print(*ans_list, sep='\n')

Solution (Python):

N = int(input())

al = [chr(ord('a') + i) for i in range(26)]

ans = ['a']
for i in range(N-1):
    tmp = []
    for s in ans:
        stop = ord(max(s)) + 1
        for i in range(ord('a'), stop+1):
            tmp.append(s + chr(i))
    ans = tmp
for s in ans:
    print(s)

Solution (Python):


N=int(input())

cand=["a"]

num=98
for i in range(N-1):
    
    temp=[]
    for item in cand:
        ma=0
        for c in item:
            ma=max(ma,ord(c))
        for i in range(ma-95):
            temp.append(item+chr(i+97))
    num+=1
    cand=temp[:]

for item in cand:
    print(item)

Solution (Python):
N=int(input())

alphabets = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j']

a="a"

def dfs(n):
  if n == 1:
    return["a"]

  if n == 2:
    return["aa","ab"]
  else:
    characters = alphabets[0:n]
    result = []
    for r in dfs(n-1):
      done = False
      for char in characters:
        if char in r:
          result.append(r + char)
        else:
          if not done:
            result.append(r + char)
            done =True
          else:
            break
    return result

print("\n".join(dfs(N)))

Solution (Python):

N = int(input())

al = [chr(ord('a') + i) for i in range(26)]

def dfs(S, i):
    if len(S) == N:
        yield S
        return
    for j in range(i):
        for w in dfs(S + al[j], i):
            yield w
    for w in dfs(S + al[i], i + 1):
        yield w

for w in dfs('', 0):
    print(w)

Solution (Python):

N = int(input())

al = [chr(ord('a') + i) for i in range(26)]

def dfs(S, i):
    if len(S) == N:
        yield ''.join(S)
        return
    for j in range(i):
        for w in dfs(S + [al[j]], i):
            yield w
    for w in dfs(S + [al[i]], i + 1):
        yield w

for w in dfs([], 0):
    print(w)

Solution (Python):


N = int(input())
alphabets = 'abcdefghij'

def dfs(s, mx):
    if len(s) == N:
        print("".join(s))
    else:
        t = min(len(set(s))+1,len(s)+1)
        for c in range(t):
            dfs(s + [alphabets[c]], c)

if __name__ == "__main__":
    dfs([], 0)

Solution (Python):
n = int(input())

def dfs(s, mx):
    if len(s) == n:
        print(s)
    else:
        for i in range(ord("a"), ord(mx)+2):
            tmp = s + chr(i)
            dfs(tmp, max(mx, chr(i)))
dfs("a", "a")

Solution (Python):

n = int(input())

q = ['a']
for i in range(n-1):
    nq=[]
    for j in q:
        stop=ord(max(j))+2

        for k in range(ord('a'),stop):
            nq.append(j+chr(k))
        q=nq

for i in q:
    print(i)

Solution (Python):
from collections import deque
d = 'abcdefghijklmnopqrstuvwxyz'
n = int(input())
ans = []
def dfs(x):

    que = deque(['a'])
    cnt = 1
    while len(que) != 0:
        val = que.pop()
        
        if len(val) != x:
            t = list(val)
            t.sort()
            cnt = ord(t[-1]) - ord('a')
            for i in range(cnt+2):
                que.append(val+d[i])
        else:
            ans.append(val)
    ans.sort()
    return ans

ans = dfs(n)
for i in range(len(ans)):
    print(ans[i])

Solution (Python):
def dfs(base, dic, swap, ma):
    if len(base) == ma:
        print(base)
    else:
        num = max(map(lambda x: swap[x], base)) + 1
        for i in range(num + 1):
            dfs(base + dic[i], dic, swap, ma)


n = int(input().strip())
dic = {0: "a",
       1: "b",
       2: "c",
       3: "d",
       4: "e",
       5: "f",
       6: "g",
       7: "h",
       8: "i",
       9: "j",
       }
swap = {v: k for k, v in dic.items()}
dfs("a", dic, swap, n)

Solution (Python):
N = int(input())
w = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j']


def dfs(s, i):
    
    if len(s) == N:
        print(s)
    else:
        for k in range(i+2):
            if k == i+1:
                dfs(s+w[k], i+1)
            else:
                dfs(s+w[k], i)


x = dfs('a', 0)

Solution (Python):
n = int(input())
def dfs(s,c):
    if len(s)==n:
        print(s)
        return
    for i in range(ord("a"),ord(c)+2):
        if i>ord(c):
            dfs(s+chr(i),chr(i))
        else:
            dfs(s+chr(i),c)

dfs("a","a")

Solution (Python):
N = int(input())
if N==1:
    print("a")
    exit()
def dfs(s,cnt):
    if len(s)==N:
        return s
    for i in range(cnt+1):
        if i==cnt:
            cnt+=1
        if dfs(s+chr(ord("a")+i),cnt)!=None:
            ans.append(dfs(s+chr(ord("a")+i),cnt))
ans=[]
dfs("a",1)
ans = sorted(ans)
print(*ans)

Solution (Python):
n = int(input())
l = ['a','b','c','d','e','f','g','h','i','j']

def dfs(res,i):
    if len(res)==n:
        print(res)
        return
    for k in range(i):
        dfs(res+l[k],i)
    dfs(res+l[i],i+1)

dfs('',0)

Solution (Python):
n=int(input())
l=[[] for i in range(n)]
l[0]=[[0]]
for i in range(n-1):
  for j in l[i]:
    for k in range(max(j)+2):
      l[i+1].append(j+[k])

for i in range(len(l[n-1])):
  for j in range(n):
    print(chr(l[n-1][i][j]+97), end="")
  print()

Solution (Python):
N = int(input())
chl = "abcdefghijk"
chli = {
  'a':0,
  'b':1,
  'c':2,
  'd':3,
  'e':4,
  'f':5,
  'g':6,
  'h':7,
  'i':8,
  'j':9
}

def ret(M):
  if M == 1:
    return "a"
  retl = []
  for stra in ret(M-1):
    maxi = min(chli[sorted(stra)[-1]] + 2, 10)
    cand = chl[:maxi]
    for ch in cand:
      retl.append(stra + ch)
  return retl

ans = ret(N)

for x in ans:
  print(x)

Solution (Python):
n = int(input())
l = ['a','b','c','d','e','f','g','h','i','j']

def dfs(res,i):
    if len(res)==n:
        print(res)
        return
    for k in range(i):
        dfs(res+l[k],i)
    dfs(res+l[i],i+1)

dfs('',0)

Solution (Python):
N=int(input())
alphabets = [chr(ord('a') + x) for x in range(26)]
def dfs(n,s,maxc):
    if len(s)==N:
        print(''.join(s))
        return
    for i in range(maxc+1):
        dfs(n+1,s+[alphabets[i]],maxc+1 if i==maxc else maxc)
s=[]
dfs(0,s,0)

Solution (Python):
N=int(input())
alphabets = [chr(ord('a') + x) for x in range(26)]
def dfs(n,s,maxc):
    if len(s)==N:
        print(''.join(s))
        return True
    for i in range(maxc+1):
        if i==maxc:
            maxc+=1
        dfs(n+1,s+[alphabets[i]],maxc)
s=[]
dfs(0,s,0)

Solution (Python):
from string import ascii_lowercase as alph

def gen_pattern(N, pre="", m=0):
  if len(pre)+1 == N:
    for c in alph[:m+1]:
      yield pre+c
  else:
    for c in alph[:m]:
      yield from gen_pattern(N, pre+c, m)
    yield from gen_pattern(N, pre+alph[m], m+1)

for pattern in gen_pattern(int(input())):
  print(pattern)