100711: [AtCoder]ABC071 B - Not Found
Memory Limit:256 MB
Time Limit:2 S
Judge Style:Text Compare
Creator:
Submit:0
Solved:0
Description
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