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

Solution (Python):
import string


def main():
    S = input()
    _str = set(S)
    lower_set = set(string.ascii_lowercase)
    if _str == lower_set:
        print("None")
    else:
        no_exists = list(lower_set - _str)
        print(sorted(no_exists)[0])


if __name__ == '__main__':
    main()

Solution (Python):
import string

S = str(input())

a = set(S)
b = set(string.ascii_lowercase)
c = b - a
if len(list(c)) == 0:
    print(None)
else:
    print(sorted(list(c))[0])

Solution (Python):
def main():
    S = input()

    for i in range(97, 123):
        if not chr(i) in S:
            ans = chr(i)
            break
    else:
        ans = 'None'

    print(ans)

main()

Solution (Python):
S = input()
L = [chr(i) for i in range(97,97+26)]

for c in L:
    if c in S:
        if c == 'z':
            print('None')
        continue
    else:
        print(c)
        break

Solution (Python):
S = input()

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"]

ans = ""
for i in range(len(S)):
    if S[i] in alphabet:
        alphabet.remove(S[i])
        if len(alphabet) == 0:
            break

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

Solution (Python):



import re

alphabet = 'abcdefghijklmnopqrstuvwxyz'

s = raw_input()

status = len(alphabet)

for i in range(len(alphabet)):
    if not re.search(alphabet[i],s):
        status = i
        break

if status == len(alphabet):
    print 'None'
else:
    print alphabet[status]

Solution (Python):
s = str(raw_input())
alphabets, result = "abcdefghijklmnopqrstuvwxyz", "None"
for i in range(26):
    if alphabets[i] not in s:
        result = alphabets[i]
        break
print(result)

Solution (Python):
s = input().strip()

alphabets = 'abcdefghijklmnopqrstuvwxyz'

s_set = set(s)

for c in alphabets:
    if c not in s_set:
        print(c)
        exit()
print('None')

Solution (Python):


S=input()
ans='None'
for chr_num in range(ord('a'),ord('z')+1,1):
    mozi=chr(chr_num)
    if not(mozi in S):
        ans=mozi
        break

print(ans)

Solution (Python):
import string
s = list(input())
flag = 0

for a in string.ascii_lowercase:
    if a not in s:
        print(a)
        flag = 1
        break

if flag == 0:
    print("None")

Solution (Python):
S=set(input())
k=0
for i in range(97, 97+26):
    s0=set(chr(i))
    if(not(s0.issubset(S)) and k==0):
        k=chr(i)
        break
    
if(k!=0):
    print(k)
else:
    print("None")

Solution (Python):
S = list(input())

T = list('abcdefghijklmnopqrstuvwxyz')

sub = [c for c in T if c not in S]
if len(sub) != 0:
    print(sub[0])
else:
    print('None')

Solution (Python):
import sys
inp = lambda t: t(sys.stdin.readline().strip())
inpm = lambda t: map(t, sys.stdin.readline().split())
inpl = lambda t: list(map(t, sys.stdin.readline().split()))

s = inp(str)

p = set()
for i in s:
	if i not in p:
		p.add(i)

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

Solution (Python):
S = input()

for i in "abcdefghijklmnopqrstuvwxyz":
    if S.replace(i,"") == S:
        print(i)
        break
else:
    print("None")

Solution (Python):

txt = input()
for c in 'abcdefghijklmnopqrstuvwxyz':
    if c not in txt:
        print(c)
        break
else:
    print('None')

Solution (Python):
import string

standard_let = string.ascii_lowercase

s = input()
for i in standard_let:
    if i not in s:
        print(i)
        break
else:
    print('None')

Solution (Python):
s=set(raw_input())
res = 'None'
for i in 'abcdefghijklmnopqrstuvwxyz' :
    if i not in s :
        res = i
        break
print res

Solution (Python):

s = list(input())

c = [chr(i) for i in range(97, 97+26)]
ans = "None"
for ci in c:
    if( ci not in list(s) ):
        ans = ci
        break
print(ans)

Solution (Python):
s = set(input())
alp = set('abcdefghijiklmnopqrstuvwxyz')
try:
	print(sorted(list(alp - s))[0])
except:
	print('None')

Solution (Python):

s = input()

import sys

N = 26

ary = [False for i in range(N)]

for a in s:
    ary[ord(a) - ord('a')] = True
for i, a in enumerate(ary):
    if not a:
        print(chr(i + ord('a')))
        sys.exit()

print("None")

Solution (Python):
string=raw_input()
allist=['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']
ans='None'
for i in range(len(allist)):
    if allist[i] not in string:
        ans=allist[i]
        break
print ans

Solution (Python):
import string
S = input()
diff = set(string.ascii_lowercase) - set(S)
diff = sorted(list(diff))
if len(diff) == 0:
    print('None')
else:
    print(diff[0])

Solution (Python):
s = input()
alph = [chr(i) for i in range(97,97+26)]

for i in alph:
    if i not in s:
        print(i)
        break
    if i=='z':
        print("None")

Solution (Python):
S=list(str(input()))

a=list('abcdefghijklmnopqrstuvwxyz')

for i in a:
    if i not in S:
        print(i)
        exit()
else:
    print('None')

Solution (Python):
S = input()
for i in range(26):
    a = chr(ord('a') + i)
    if not a in S:
        print(a)
        break
else:
    print('None')

Solution (Python):



def main():
    s = input()
    chars = set(s)

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


if __name__ == '__main__':
    main()

Solution (Python):


s = input()
s = set(list(s))

ans = 'None'

for alpha in list('abcdefghijklmnopqrstuvwxyz'):
    if alpha not in s:
        ans = alpha
        break

print(ans)

Solution (Python):
S = input()

alphabet = "abcdefghijklmnopqrstuvwxyz"

for alp in alphabet:
    if alp not in S:
        print(alp)
        break
else:
    print("None")