Buggy python submission (verdict: Time Limit Exceeded):
from itertools import product

N = int(input())
added = set()
ans = []
a = [[chr(97+i) for i in range(j)] for j in range(1,N+1)]
for x in product(*a):
    appeared = set('a')
    d = ['a']
    temp = [0]
    for y in x[1:]:
        if y not in appeared:
            appeared.add(y)
            d.append(y)
            temp.append(d.index(y))
        else:
            temp.append(d.index(y))
    t = tuple(temp)
    if t not in added:
        print(''.join(x))
        added.add(t)

Fixed submission:
def dfs(s,n):
    if len(s) == n:
        print(s)
    else:
        for i in range(len(set(s))+1):
            dfs(''.join([s,chr(97+i)]),n)

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

Buggy python submission (verdict: Time Limit Exceeded):
from itertools import product

N = int(input())
added = set()
ans = []
a = [[chr(97+i) for i in range(j)] for j in range(1,N+1)]
for x in product(*a):
    appeared = set('a')
    d = ['a']
    temp = [0]
    for y in x[1:]:
        if y not in appeared:
            appeared.add(y)
            d.append(y)
            temp.append(d.index(y))
        else:
            temp.append(d.index(y))
    t = tuple(temp)
    if t not in added:
        print(''.join(x))
        added.add(t)

Fixed submission:
def dfs(s,n):
    if len(s) == n:
        print(s)
    else:
        for i in range(len(set(s))+1):
            dfs(''.join([s,chr(97+i)]),n)

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

Buggy python submission (verdict: Time Limit Exceeded):
from itertools import product

N = int(input())
added = set()
ans = []
a = [[i for i in range(j)] for j in range(1,N+1)]
for x in product(*a):
    count = 0
    appeared = set()
    temp = []
    order = [float('inf')] * N
    for y in x:
        if y not in appeared:
            order[y] = 97 + count
            count += 1
            appeared.add(y)
            temp.append(chr(order[y]))
        else:
            temp.append(chr(order[y]))
    s = ''.join(temp)
    if s not in added:
        ans.append(s)
        added.add(s)
print('\n'.join(ans))

Fixed submission:
def dfs(s,n):
    if len(s) == n:
        print(s)
    else:
        for i in range(len(set(s))+1):
            dfs(''.join([s,chr(97+i)]),n)

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

Buggy python submission (verdict: Time Limit Exceeded):
from itertools import product

N = int(input())
added = set()
ans = []
a = [[i for i in range(j)] for j in range(1,N+1)]
for x in product(*a):
    count = 0
    appeared = set()
    temp = []
    order = [float('inf')] * N
    for y in x:
        if y not in appeared:
            order[y] = 97 + count
            count += 1
            appeared.add(y)
            temp.append(chr(order[y]))
        else:
            temp.append(chr(order[y]))
    s = ''.join(temp)
    if s not in added:
        ans.append(s)
        added.add(s)
print('\n'.join(sorted(ans)))

Fixed submission:
def dfs(s,n):
    if len(s) == n:
        print(s)
    else:
        for i in range(len(set(s))+1):
            dfs(''.join([s,chr(97+i)]),n)

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

Buggy python submission (verdict: Time Limit Exceeded):
from itertools import product

N = int(input())
added = set()
ans = []
a = [[i for i in range(j)] for j in range(1,N+1)]
for x in product(*a):
    count = 0
    appeared = set()
    temp = []
    order = [float('inf')] * N
    for y in x:
        if y not in appeared:
            order[y] = 97 + count
            count += 1
            appeared.add(y)
            temp.append(chr(order[y]))
        else:
            temp.append(chr(order[y]))
    s = ''.join(temp)
    if s not in added:
        ans.append(s)
        added.add(s)
for x in sorted(ans):
    print(x)

Fixed submission:
def dfs(s,n):
    if len(s) == n:
        print(s)
    else:
        for i in range(len(set(s))+1):
            dfs(''.join([s,chr(97+i)]),n)

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

Buggy python submission (verdict: Time Limit Exceeded):
from itertools import product

N = int(input())
added = set()
ans = []
a = [[i for i in range(j)] for j in range(1,N+1)]
for x in product(*a):
    count = 0
    appeared = set()
    temp = []
    order = [float('inf')] * N
    for y in x:
        if y not in appeared:
            order[y] = 97 + count
            count += 1
            appeared.add(y)
            temp.append(chr(order[y]))
        else:
            temp.append(chr(order[y]))
    s = ''.join(temp)
    if s not in added:
        ans.append(s)
        added.add(s)
for x in sorted(ans):
    print(x)

Fixed submission:
def dfs(s,n):
    if len(s) == n:
        print(s)
    else:
        for i in range(len(set(s))+1):
            dfs(''.join([s,chr(97+i)]),n)

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