Problem:


Score : 200 points

Problem Statement

You are given a string S consisting of lowercase English letters.
Find the lexicographically (alphabetically) smallest lowercase English letter that does not occur in S.
If every lowercase English letter occurs in S, print None instead.

Constraints

1 \leq |S| \leq 10^5 (|S| is the length of string S.)

S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

Print the lexicographically smallest lowercase English letter that does not occur in S.
If every lowercase English letter occurs in S, print None instead.

Sample Input 1

atcoderregularcontest

Sample Output 1

b

The string atcoderregularcontest contains a, but does not contain b.

Sample Input 2

abcdefghijklmnopqrstuvwxyz

Sample Output 2

None

This string contains every lowercase English letter.

Sample Input 3

fajsonlslfepbjtsaayxbymeskptcumtwrmkkinjxnnucagfrg

Sample Output 3

d



Sample input:
atcoderregularcontest


Sample output:
b

Submission status: Accepted

Solution code:
#
# abc071 b
#
import sys
from io import StringIO
import unittest


class TestClass(unittest.TestCase):
    def assertIO(self, input, output):
        stdout, stdin = sys.stdout, sys.stdin
        sys.stdout, sys.stdin = StringIO(), StringIO(input)
        resolve()
        sys.stdout.seek(0)
        out = sys.stdout.read()[:-1]
        sys.stdout, sys.stdin = stdout, stdin
        self.assertEqual(out, output)

    def test_入力例_1(self):
        input = """atcoderregularcontest"""
        output = """b"""
        self.assertIO(input, output)

    def test_入力例_2(self):
        input = """abcdefghijklmnopqrstuvwxyz"""
        output = """None"""
        self.assertIO(input, output)

    def test_入力例_3(self):
        input = """fajsonlslfepbjtsaayxbymeskptcumtwrmkkinjxnnucagfrg"""
        output = """d"""
        self.assertIO(input, output)


def resolve():
    S = input()
    n = [0 for _ in range(26)]
    for i in range(len(S)):
        n[ord(S[i]) - ord("a")] = 1
    for i in range(26):
        if n[i] == 0:
            print(chr(ord("a")+i))
            break
    else:
        print("None")


if __name__ == "__main__":
    # unittest.main()
    resolve()

Submission status: Accepted

Solution code:
s=input()
a=ord("a")
for i in range(26):
  if chr(a+i) in s:
    pass
  else:
    print(chr(a+i))
    break
else:
  print("None")

Submission status: Accepted

Solution code:
from sys import stdin

s = stdin.readline().strip()
a = set('abcdefghijklmnopqrstuvwxyz')
b = a - set(s)

if len(b) == 0: print('None')
else: print(min(b))

Submission status: Accepted

Solution code:
def main():
	S = input()
	lst = [False] * 26

	for ch in S:
		lst[ord(ch) - ord("a")] = True

	for i in range(26):
		if lst[i] == False:
			print(chr(i + ord("a")))
			break
	else:
		print("None")

  
if __name__ == "__main__":
  	main()

Submission status: Accepted

Solution code:
S = set(input())
a = set([chr(i) for i in range(ord('a'), ord('z')+1)])
result = sorted(list(a-S))
if len(result) == 0:
    print('None')
else:
    print(result[0])

Submission status: Accepted

Solution code:
s = list(input())
s = list(set(s))
s.sort()
if len(s) == 26:
    print("None")
l = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]
for i in range(26):
    if len(s) <= i:
        print(l[i])
        break
    if s[i] != l[i]:
        print(l[i])
        break

Submission status: Accepted

Solution code:
ans = []
s = input()
for i in range(26):ans.append(0)
for i in s:
  ans[ord(i)-97] = 1
for i in range(26):
  if(ans[i]==0):print(chr(97+i));exit()
print("None")

Submission status: Accepted

Solution code:
s = str(input())
moji = 'abcdefghijklmnopqrstuvwxyz'
dic = {}
for i in range(len(moji)):
    dic.setdefault(moji[i],0)
for i in range(len(s)):
    dic[s[i]] += 1
isNone = True
for i in range(len(moji)):
    if dic[moji[i]]==0:
        print(moji[i])
        isNone = False
        break
if isNone:
    print('None')

Submission status: Accepted

Solution code:
s = list(input())
s = set(s)
m = 'abcdefghijklmnopqrstuvwxyz'
for i in range(len(m)):
    if not m[i] in s:
        print(m[i])
        exit(0)
print('None')

Submission status: Accepted

Solution code:
S = list(input())
a = [chr(i) for i in range(97, 97 + 26)]

for a in a:
    if S.count(a) == 0:
        print(a)
        break
else:
    print(None)

Submission status: Accepted

Solution code:
alp = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z']
s1 = str(input())
s = []
for i in s1:
    s.append(i)
s = list(set(s))
s.sort()
x = 'None'
for h in alp:
    if h not in s:
        x = h
        break
print(x)

Submission status: Accepted

Solution code:
s1 = list(input())
s2 = list('abcdefghijklmnopqrstuvwxyz')
r = sorted(list(set(s2) - set(s1)))
if len(r) == 0:
  print("None")
else:
  print(r[0])

Submission status: Accepted

Solution code:
#B - Not Found
S = list(input())
S = sorted(S)
S = set(S)

A = [chr(o) for o in range(ord('a'),ord('z')+1)]
result = 'None'
for i in A:
    if i in S:
        continue
    else:
        result = i
        break
print(result)

Submission status: Accepted

Solution code:
S = input()
flag = True

while True:
  if S.count('a') == 0:
    ans = 'a'
    break
  elif S.count('b') == 0:
    ans = 'b'
    break
  elif S.count('c') == 0:
    ans = 'c'
    break
  elif S.count('d') == 0:
    ans = 'd'
    break
  elif S.count('e') == 0:
    ans = 'e'
    break
  elif S.count('f') == 0:
    ans = 'f'
    break 
  elif S.count('g') == 0:
    ans = 'g'
    break
  elif S.count('h') == 0:
    ans = 'h'
    break
  elif S.count('i') == 0:
    ans = 'i'
    break
  elif S.count('j') == 0:
    ans = 'j'
    break
  elif S.count('k') == 0:
    ans = 'k'
    break
  elif S.count('l') == 0:
    ans = 'm'
    break
  elif S.count('n') == 0:
    ans = 'n'
    break
  elif S.count('o') == 0:
    ans = 'o'
    break
  elif S.count('p') == 0:
    ans = 'p'
    break
  elif S.count('q') == 0:
    ans = 'q'
    break
  elif S.count('r') == 0:
    ans = 'r'
    break
  elif S.count('s') == 0:
    ans = 's'
    break
  elif S.count('t') == 0:
    ans = 't'
    break
  elif S.count('u') == 0:
    ans = 'u'
    break
  elif S.count('v') == 0:
    ans = 'v'
    break
  elif S.count('w') == 0:
    ans = 'w'
    break
  elif S.count('x') == 0:
    ans = 'x'
    break
  elif S.count('y') == 0:
    ans = 'y'
    break
  elif S.count('z') == 0:
    ans = 'z'
    break
  else:
    ans = 'None'
    break
print(ans)

Submission status: Accepted

Solution code:
S = input()
s = [ True ] * 26
for i in range(len(S)):
    s[ord(S[i])-97] = False
for i in range(26):
    if s[i]:
        print(chr(i+97))
        exit()
print(None)

Submission status: Accepted

Solution code:
S=input()
l=[0]*26
for i in range(len(S)):
  l[ord(S[i])-97]+=1
for j in range(26):
  if l[j]==0:
    print(chr(j+97))
    break
else:
  print("None")

Submission status: Accepted

Solution code:
S = input()
S_set = set(S)

for i in range(97,123):
    if chr(i) not in S_set:
        print(chr(i))
        exit()
print("None")

Submission status: Accepted

Solution code:
S = input()

ls = list("abcdefghijklmnopqrstuvwxyz")

ans = "None"

for chara in ls:
  if S.count(chara) == 0:
    ans = chara
    break
print(ans)

Submission status: Accepted

Solution code:
from string import ascii_lowercase
S=input()
ABC=[i for i in ascii_lowercase]
# print(ABC)

for i in ABC:
  if not i in S:
    print(i)
    break
else:
  print('None')

Submission status: Accepted

Solution code:
#k = int(input())
#s = input()
#a, b = map(int, input().split())
#s, t = map(str, input().split())
#l = list(map(int, input().split()))
#l = [list(map(int,input().split())) for i in range(n)]
#a = [list(input()) for _ in range(n)]
#a = [int(input()) for _ in range(n)]



s = input()

h = {}

alp = "abcdefghijklmnopqrstuvwxyz"

for i in alp:
    h[i] = 0

for i in s:
    h[i] += 1

#print(h)
for k,v in h.items():
    if (v == 0):
        print(k)
        exit()

print("None")

Submission status: Accepted

Solution code:
#k = int(input())
#s = input()
#a, b = map(int, input().split())
#s, t = map(str, input().split())
#l = list(map(int, input().split()))
#l = [list(map(int,input().split())) for i in range(n)]
#a = [list(input()) for _ in range(n)]
#a = [int(input()) for _ in range(n)]


#hashでカウンタを格納する
#ソートして、要素がインクリメントされない箇所を検出する: → 要素がaa

s = input()

h = {"a":0,"b":0,"c":0,"d":0,"e":0,"f":0,"g":0,"h":0,"i":0,"j":0,"k":0,"l":0,"m":0,"n":0,"o":0,"p":0,"q":0,"r":0,"s":0,"t":0,"u":0,"v":0,"w":0,"x":0,"y":0,"z":0}

for i in s:
    h[i] += 1

#print(h)
for k,v in h.items():
    if (v == 0):
        print(k)
        exit()

print("None")

Submission status: Accepted

Solution code:
S = input()
alf = 'abcdefghijklmnopqrstuvwxyz'

s = set()
a = set()

for i in range(len(S)):
  s.add(S[i])
for i in range(len(alf)):
  a.add(alf[i])

str = ''
hoge = a ^ s
for h in hoge:
  str += h
  
str=sorted(str)
if str:
  print(str[0])
else:
  print('None')

Submission status: Accepted

Solution code:
S=input()
set1=set(S)

for i in range(97,123):
  if chr(i) not in set1:
    print(chr(i))
    exit()
print('None')

Submission status: Accepted

Solution code:
a = list(input())
done = False
for s in list('abcdefghijklmnopqrstuvwxyz'):
  if a.count(s) == 0 and not done:
    print(s)
    done = True

if not done:
  print("None")

Submission status: Accepted

Solution code:
S = list(input())
alf = 'abcdefghijklmnopqrstuvwxyz'
ans = 'None'
for i in range(len(alf)):
    if not alf[i] in S:
        ans = alf[i]
        break
print(ans)

Submission status: Accepted

Solution code:
s = input()
for i in range(97,123):
	if chr(i) not in s:
		print(chr(i))
		exit()
print('None')

Submission status: Accepted

Solution code:
s = input()
for i in range(97,97 + 26):
	if chr(i) not in  s:
		print(chr(i))
		exit()
print('None')

Submission status: Accepted

Solution code:
S = set(input())
Flag = [True]*26

for i in S:
  Flag[ord(i)-97] = False

for i in range(26):
  if Flag[i]:
    print(chr(97+i))
    exit()

print("None")

Submission status: Accepted

Solution code:
s = list(input())
c = 0
for i in range(97,97 + 26):
	if chr(i) not in  s:
		print(chr(i))
		break
	c += 1
if c == 26:
  print('None')

Submission status: Accepted

Solution code:
s=list(input())
s=set(s)

for i in range(26):
	if chr(97+i) not in s:
		print(chr(97+i))
		exit()

print('None')

Submission status: Accepted

Solution code:
import string
al = string.ascii_lowercase

S = set(input())

for i in al:
  if i not in S:
    print(i)
    exit()

print("None")

Submission status: Accepted

Solution code:
S=list(set(input()))
S.sort()
import string
switch=True
A=list(string.ascii_lowercase)
for i in A:
    if not i in S:
        print(i)
        switch=False
        break
if switch:
    print("None")

Submission status: Accepted

Solution code:
S = input().strip()
for s in "abcdefghijklmnopqrstuvwxyz":
    if not s in S:
        print(s)
        exit()
print("None")

Submission status: Accepted

Solution code:
import bisect, collections, copy, heapq, itertools, math, string, sys
input = lambda: sys.stdin.readline().rstrip() 
sys.setrecursionlimit(10**7)
INF = float('inf')
def I(): return int(input())
def F(): return float(input())
def SS(): return input()
def LI(): return [int(x) for x in input().split()]
def LI_(): return [int(x)-1 for x in input().split()]
def LF(): return [float(x) for x in input().split()]
def LSS(): return input().split()

def resolve():
    S = SS()

    ans = 'None'
    for i in string.ascii_lowercase:
        if S.count(i) == 0:
            ans = i
            break

    print(ans)

if __name__ == '__main__':
    resolve()

Submission status: Accepted

Solution code:
import string
S = set(input())
for c in string.ascii_lowercase:
    if c not in S:
        print(c)
        break
else:
    print('None')

Submission status: Accepted

Solution code:
import sys


inint = lambda: int(sys.stdin.readline())
inintm = lambda: map(int, sys.stdin.readline().split())
inintl = lambda: list(inintm())
instrm = lambda: map(str, sys.stdin.readline().split())
instrl = lambda: list(instrm())

s = input()
sl = []

for i in range(len(s)):
    sl.append(s[i])

for i in range(97, 123):
    if chr(i) not in sl:
        print(chr(i))
        exit()

print("None")

Submission status: Accepted

Solution code:
al = list("abcdefghijklmnopqrstuvwxyz")

s = list(input())
for i in s:
    if i in al:
        del al[al.index(i)]
        
if len(al) == 0:
    print("None")
else:
    print(al[0])

Submission status: Accepted

Solution code:
from string import ascii_lowercase

S = input()
string = ascii_lowercase
for s in string:
    if s not in S:
        print(s)
        exit()
print('None')

Submission status: Accepted

Solution code:
s = input()

a=[0]*200
flag=0
for i in s:
    a[ord(i)]=i
for i in range(ord("a"),ord("z")+1):
    if a[i]==0:
        print(chr(i))
        flag=1
        break
print("None" if flag==0 else "")

Submission status: Accepted

Solution code:
S = set(input())
alp = 'abcdefghijklmnopqrstuvwxyz'

for a in alp:
    if not a in S:
        print(a)
        break
else:
    print('None')

Submission status: Accepted

Solution code:
S = input()

chars = set()
all_chars = set([c for c in 'abcdefghijklmnopqrstuvwxyz'])

for c in S:
    chars.add(c)

diff = list(all_chars - chars)
diff = sorted(diff)

if len(diff) == 0:
    print(None)
else:
    print(diff[0])

Submission status: Accepted

Solution code:
S = input()

S = set(S)
flag = True
alphabet = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
for i in alphabet:
    if i not in S:
        print(i)
        flag = False
        break
if flag:
    print("None")

Submission status: Accepted

Solution code:
str1 = input()
li = list(str1)
anli = []
for i in range(26):
    anli.append(0)
for i in range(len(li)):
   anli[ord(li[i]) - 97] += 1
flag = True
mi = 27
for i in range(len(anli)):
    if anli[i] == 0:
        flag = False
        mi = min(i,mi)
if flag:
    print('None')
else:
    print(chr(mi+97))

Submission status: Accepted

Solution code:
S = input()

for i in range(ord("a"), ord("z")+1):
    if(chr(i) not in S):
        print(chr(i))
        break
else:
    print("None")

Submission status: Accepted

Solution code:
S = input()

for alph in 'abcdefghijklmnopqrstuvwxyz':
    if alph not in S:
        print(alph)
        exit()

print('None')

Submission status: Accepted

Solution code:
s=list(input())
n=len(s)
l=list("abcdefghijklmnopqrstuvwxyz")
l.append("None")
for i in range(n):
    if s[i] in l:
        l.remove(s[i])
print(l[0])

Submission status: Accepted

Solution code:
s = input()
ascii_lowercase = list('abcdefghijklmnopqrstuvwxyz')
s = list(s)
s = set(s)
s = list(s)
s = sorted(s)
n = len(s)
flag = 0

for i in range(n):
    if s[i] != ascii_lowercase[i]:
        print(ascii_lowercase[i])
        flag = 1
        break

if len(s) != len(ascii_lowercase) and flag != 1:
    print(ascii_lowercase[len(s)])
elif flag != 1:
    print('None')

Submission status: Accepted

Solution code:
S = input()

abc = "abcdefghijklmnopqrstuvwxyz"

dic = {s: True for s in abc}

for s in S:
    if dic[s]:
        dic[s] = False

for d in dic:
    if dic[d]:
        print(d)
        exit()

print("None")

Submission status: Accepted

Solution code:
import string
s = input()
for c in string.ascii_lowercase:
  if c not in s:
    print(c)
    quit()
print("None")

Submission status: Accepted

Solution code:
s=input()
res="None"
for i in range(97,123):
    if not chr(i) in s:
        res=chr(i)
        break
print(res)

Submission status: Accepted

Solution code:
t=list((set(list(str(input())))))
t.sort(reverse=False)
al = ('abcdefghijklmnopqrstuvwxyz')
alll=list(al)
for a in alll:
    if a not in t:
        print(a)
        exit()
print('None')

Submission status: Accepted

Solution code:
import sys
def input(): return sys.stdin.readline().strip()

def main():
    S = input()
    d = set()
    for c in S: d.add(c)
    for i in range(26):
        if chr(i + 97) not in d:
            print(chr(i + 97))
            return
    print("None")
    
    


if __name__ == "__main__":
    main()

Submission status: Accepted

Solution code:
# # Make IO faster
# import sys
# input = sys.stdin.readline

# # get single (or) multiple str
# X = input()

# # get single int
# N = int(input())
# # get multiple int (e.g., 2)
# X, Y = map(int, input().split())
# # get multiple int (e.g., 2) for N lines
# XY = [list(map(int, input().split())) for _ in range(N)]

# from IPython import embed; embed(); exit();

# 全部入り
import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
from itertools import accumulate, permutations, combinations, product
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from fractions import gcd
from heapq import heappush, heappop
from functools import reduce
import numpy as np
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

from string import ascii_lowercase
X = {c for c in ascii_lowercase}
S = input()
for s in S:
    if s in X:
        X.remove(s)
X = sorted(X)
if len(X) == 0:
    print("None")
else:
    print(X[0])

Submission status: Accepted

Solution code:
S = set(input())
all_ = []
for i in range(97,123):
    all_.append(chr(i))
sa = list(set(all_) - S)
sa.sort()
if sa:
    print(sa[0])
else:
    print('None')

Submission status: Accepted

Solution code:
S=input()
x="None"
num=[False for i in range(26)]
for i in range(len(S)):
    num[ord(S[i])-ord("a")]=True

for j in range(26):
    if not num[j]:
        x=chr(j+ord("a"))
        break

print(x)

Submission status: Accepted

Solution code:
S=input()
x="None"
T="abcdefghijklmnopqrstuvwxyz"
num=[0 for i in range(26)]
for i in range(26):
    num[i]+=S.count(T[i])

for j in range(26):
    if num[j]==0:
        x=T[j]
        break

print(x)

Submission status: Accepted

Solution code:
import sys, re
from math import ceil, floor, sqrt, pi, factorial, gcd
from copy import deepcopy
from collections import Counter, deque
from heapq import heapify, heappop, heappush
from itertools import accumulate, product, combinations, combinations_with_replacement
from bisect import bisect, bisect_left, bisect_right
from functools import reduce
from decimal import Decimal, getcontext
# input = sys.stdin.readline 
def i_input(): return int(input())
def i_map(): return map(int, input().split())
def i_list(): return list(i_map())
def i_row(N): return [i_input() for _ in range(N)]
def i_row_list(N): return [i_list() for _ in range(N)]
def s_input(): return input()
def s_map(): return input().split()
def s_list(): return list(s_map())
def s_row(N): return [s_input for _ in range(N)]
def s_row_str(N): return [s_list() for _ in range(N)]
def s_row_list(N): return [list(s_input()) for _ in range(N)]
def lcm(a, b): return a * b // gcd(a, b)
sys.setrecursionlimit(10 ** 6)
INF = float('inf')
MOD = 10 ** 9 + 7
num_list = []
str_list = []

def main():
    s = s_input()

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

    for al in alpabet:
        if al not in s:
            ans_list.append(al)

    print(ans_list[0] if len(ans_list) > 0 else 'None')

if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
S = input()
alph="abcdefghijklmnopqrstuvwxyz"
for i in alph:
  if i not in S:
    print(i)
    exit()
print("None")

Submission status: Accepted

Solution code:
S = input()
dic = {}

for s in S:
  dic[ord(s)] = True
  
for i in range(97, 97+26):
  if i not in dic:
    print(chr(i))
    exit()

print('None')

Submission status: Accepted

Solution code:
s=set(input())
for i in range(97,97+26):
    c=chr(i)
    if not c in s:
        print(c)
        exit()
print('None')

Submission status: Accepted

Solution code:
s = list(sorted(set(input())))
lst = [chr(i) for i in range(97, 97+26)]

for i in lst:
    if not(i in s):
        print(i)
        exit()
else:
    print("None")

Submission status: Accepted

Solution code:
S = input()
a = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z']

for i in S:
    if i in a:
        a.remove(i)
#print(a)
print(a[0] if len(a)!=0 else 'None')

Submission status: Accepted

Solution code:
import string

s = set(input())
alphabets = set(string.ascii_lowercase)

l = sorted(list(alphabets - s))

if len(l) == 0:
  print('None')
else:
  print(l[0])

Submission status: Accepted

Solution code:
s_list = list(input())

result = None

for s_uni in range(ord('a'), ord('z') + 1):
    if not chr(s_uni) in s_list:
        result = chr(s_uni)
        break

if result:
    print(result)
else:
    print('None')

Submission status: Accepted

Solution code:
S = set(input())
Flag = False
for T in range(26):
    Le = chr(ord('a')+T)
    if Le not in S:
        Flag = True
        break
if Flag:
    print(Le)
else:
    print('None')

Submission status: Accepted

Solution code:
import sys
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
read = sys.stdin.buffer.read
sys.setrecursionlimit(10 ** 7)
INF = float('inf')

S = input()

set_ = set(S)
for c in [chr(i) for i in range(97, 97+26)]:
    if c not in set_:
        print(c)
        quit()
print('None')

Submission status: Accepted

Solution code:
CASES = "abcdefghijklmnopqrstuvwxyz"
s=set(input())
for c in CASES:
  if c not in s:
    print(c)
    exit()
print("None")

Submission status: Accepted

Solution code:
import sys
from string import ascii_lowercase as alphabets
from collections import defaultdict

readline=sys.stdin.readline

s=readline().strip()
d=defaultdict(int)
for x in s:
  d[x]=1
for a in alphabets:
  if d[a]==0:
    print(a)
    sys.exit()
print('None')

Submission status: Accepted

Solution code:
Sset=set(input())
Sset=sorted(Sset)

ans = "None"
flg = True
last = "None"
for i,c in enumerate(Sset):
	if i+97 !=ord(c):
		flg=False
		ans = chr(i+97)
		break
	last = c

if flg and last != 'z' :
	ans = chr(ord(last)+1)
print(ans)

Submission status: Accepted

Solution code:
import sys

read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines
sys.setrecursionlimit(10 ** 9)
INF = 1 << 60
MOD = 1000000007


def main():
    S = readline().strip()

    found = [0] * 26
    for c in S:
        found[ord(c) - ord('a')] = True

    ans = 'None'
    for i, f in enumerate(found):
        if not f:
            ans = chr(i + ord('a'))
            break

    print(ans)
    return


if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
import sys
from string import ascii_lowercase

read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines
sys.setrecursionlimit(10 ** 9)
INF = 1 << 60
MOD = 1000000007


def main():
    S = readline().strip()

    s = set(S)
    for c in ascii_lowercase:
        if c not in s:
            print(c)
            return

    print('None')
    return


if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
S=[x for x in input()]
A='abcdefghijklmnopqrstuvwxyz'
for a in A:
  if a not in S:
    print(a)
    break
else:
  print('None')

Submission status: Accepted

Solution code:
moji = input()
L = len(moji)

lst = []
for i in range(L):
    lst.append(ord(moji[i]))

lst2 = list(range(97,123))
ans = list(set(lst2) - set(lst))

if len(ans) == 0:
    print("None")
else:
    print(chr(min(ans)))

Submission status: Accepted

Solution code:
d = list(input())
d.sort()

l = list("abcdefghijklmnopqrstuvwxyz")
l.remove(d[0])
for i in range(len(d)-1):
    if d[i+1] != d[i]:
        l.remove(d[i+1])
if len(l) == 0:
    print("None")
else:
    print(l[0])

Submission status: Accepted

Solution code:
s = input()

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

for i in range(len(s)):
    if s[i] in alphabet:
        alphabet.remove(s[i])

if alphabet:
    print(alphabet[0])
else:
    print('None')

Submission status: Accepted

Solution code:
S = input()
list = [chr(i) for i in range(97, 97 + 26)]
x = 0
for i in range(26):
    if list[i] in S:
        x += 1
if x == 26:
    print('None')
    exit()
for i in range(26):
    if list[i] not in S:
        print(list[i])
        exit()

Submission status: Accepted

Solution code:
S = list(input())
S.sort()
import bisect
a_uni = ord('a')

Search = S
for i in range(26):
    char = chr(a_uni+i)

    if Search and Search[0] == char:
        ind = bisect.bisect_right(S,char)
        Search = S[ind:]
        continue
    print(char)
    exit()
print('None')

Submission status: Accepted

Solution code:
S = input()

str_list = list('abcdefghijklmnopqrstuvwxyz')
str_cnt = [0 for i in range(len(str_list))]

for i in range(len(S)):
    s = S[i]
    
    index_s = str_list.index(s)
    str_cnt[index_s] += 1

if (0 not in str_cnt):
    ans = 'None'
else:
    ans = str_list[str_cnt.index(0)]

print(ans)

Submission status: Accepted

Solution code:
S=set(list(input()))
l=[chr(i+97)for i in range(26)if not chr(i+97)in S]
print(l[0]if len(l)else'None')

Submission status: Accepted

Solution code:
import collections
S=str(input())
cc=collections.Counter(S)
alphabet=['a','b','c','d','e','f','g','h','i','j','k','l','m','m','o','p','q','r','s','t','u','v','w','x','y','z']

for i in range(26):
    if cc[alphabet[i]]==0:
        print(alphabet[i])
        exit()
    if i==25:
        print('None')
        exit()

Submission status: Accepted

Solution code:
#!/usr/bin/env python3

alpha = {
    'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
}

S=set(input())
if len(S) == len(alpha):
    print("None")
else:
    print(sorted(alpha - S)[0])

Submission status: Accepted

Solution code:
s=input()
S=[]
count=0
for i in range(len(s)):
    S.append(s[i])
for x in range(26):
    if chr(x+ord("a")) in S:
        count=count+1
    else:
        print(chr(x+ord("a")))
        break
if count==26:
    print(None)
else:
    pass

Submission status: Accepted

Solution code:
S = input()
List = list(S)
s_l = set(List)
n = 10
res= ""
flag = False
for i in range(97,123):
  if not chr(i) in s_l:
    res = chr(i)
    flag = True
    break
if flag:
  print(res)
else:
  print("None")

Submission status: Accepted

Solution code:
s = set(input())
for i in range(97, 123):
    if chr(i) not in s:
        print(chr(i))
        break
else:
    print("None")

Submission status: Accepted

Solution code:
S = input()
S = set(S)
for i in range(26):
    w = chr(ord("a") + i)
    if not w in S:
        print(w)
        break
else:
    print("None")

Submission status: Accepted

Solution code:
s=list(input())
for i in range(ord('a'),ord('z')+1):
    if s.count(chr(i))==0:
        print(chr(i))
        exit()
print('None')

Submission status: Accepted

Solution code:
abc = "abcdefghijklmnopqrstuvwxyz"
a = input()
for i in range(len(abc)):
    if abc[i] not in a:
        print(abc[i])
        exit()
print("None")

Submission status: Accepted

Solution code:
s = input()

alphabets = 'abcdefghijklmnopqrstuvwxyz'
for i in s:
  alphabets = alphabets.replace(i, '')
  s = s.replace(i, '')

alphabets = [i for i in alphabets]
alphabets.sort()
if len(alphabets) > 0:
  print(alphabets[0])
else:
  print('None')

Submission status: Accepted

Solution code:
S = input()

Alpha = "abcdefghijklmnopqrstuvwxyz"
for i in Alpha:
  if i not in S:
    print(i)
    exit()
print("None")

Submission status: Accepted

Solution code:
S = input()
al = [0] * 26
s = ""

for s in S:
    al[ord(s) - 97] += 1

if 0 not in al:
    print("None")
else:
    print(chr(al.index(0) + 97))

Submission status: Accepted

Solution code:
S = str(input())
a = [0] * 26

# 数値(1〜26)→アルファベット(A〜Z)
num2alpha = lambda c: chr(c+96)

#num2alpha(3) #==> C 
# アルファベット(A〜Z)→数値(1〜26)
alpha2num = lambda c: ord(c) - ord('a') + 1

#alpha2num('Y') #==> 25 

for i in range(len(S)):
  x = alpha2num(S[i])
  a[x - 1] += 1
  
if min(a) != 0:
  print("None")
else:
  ans = a.index(0)
  print(num2alpha(ans + 1))

Submission status: Accepted

Solution code:
s = input()
for i in range(26):
    if s.count(chr(ord('a')+i)):
        continue
    else:
        print(chr(ord('a')+i))
        exit()
print('None')

Submission status: Accepted

Solution code:
import sys
sys.setrecursionlimit(4100000)
import math
import itertools
INF = 10**9

def main():
    S = input()
    alphabet = 'abcdefghijklmnopqrstuvwxyz'

    count = 0
    for s in alphabet:
        if s not in S:
            print(s)
            return
        if len(set(alphabet)- set(S)) == 0:
            print(None)
            return


if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
import sys
sys.setrecursionlimit(4100000)
import math
import itertools
INF = 10**9

def main():
    S = input()
    alphabet = 'abcdefghijklmnopqrstuvwxyz'

    S_set = set(S)
    alphabet_set = set(alphabet)

    array = list(alphabet_set - S_set)
    array.sort()
    if len(array) == 0:
        print('None')
    else:
        print(array[0])


if __name__ == '__main__':
    main()

Submission status: Accepted

Solution code:
s = set(list(input()))
strings = [chr(i) for i in range(97, 97+26)]

for i in strings:
    if not i in s:
        print(i)
        exit()
print(None)

Submission status: Accepted

Solution code:
str1 ='abcdefghijklmnopqrstuvwxyz'
N = input()
count = 0
for i in str1:
  if i not in N:
    print(i)
    count +=1
    break
if count ==0:
  print('None')

Submission status: Accepted

Solution code:
s = input()
ans = 'None'
for i in range(26):
    c = chr(ord('a') + i)
    if c not in s:
        ans = c
        break
print(ans)

Submission status: Accepted

Solution code:
s = set(input())
a = set("abcdefghijklmnopqrstuvwxyz")
d = a - s
if d:
    print(sorted(d)[0])
else:
    print("None")

Submission status: Accepted

Solution code:
s = input()
a = "abcdefghijklmnopqrstuvwxyz"

for i in s:
    a = a.replace(i, "")
else:
    if len(a):
        print(a[0])
    else:
        print("None")

Submission status: Accepted

Solution code:
s = list(str(input()))
s.sort()
a = [chr(ord('a') + i) for i in range(26)]
b = {}
for i in a:
    b[i] = 0
for i in s:
    b[i] += 1

alf = ''
for i in a:
    if b[i] == 0:
        alf = i
        break
if alf:
    print(i)
else:
    print('None')

Submission status: Accepted

Solution code:
S = input()
alp = list('abcdefghijklmnopqrstuvwxyz')
for i in range(len(S)):
  if S[i] in alp:
    alp.remove(S[i])
if len(alp) == 0:
  print('None')
else:
  print(alp[0])

Submission status: Accepted

Solution code:
from sys import exit
S = input()
for letter in 'abcdefghijklmnopqrstuvwxyz':
  if letter not in S:
    print(letter)
    exit(0)
print(None)

Submission status: Accepted

Solution code:
s = list(input())

s.sort()

ans = "None"
for i in range(97,123):
    if s.count(chr(i)) == 0:
        ans = chr(i)
        break

print(ans)

Submission status: Accepted

Solution code:
p = input()

s = list(p)
s.sort()

answer = -1

check = []
for i in range(26):
    check.append(False)

for i in range(len(s)):
    x = ord(s[i])
    check[x - 97] = True

for i in range(26):
    if not check[i]:
        answer = i + 97
        break

if answer == -1:
    print('None')
else:
    print(chr(answer))