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https://codeforces.com/contest/1925/p...

C. Did We Get Everything Covered?
time limit per test2 seconds
memory limit per test256 megabytes
inputstandard input
outputstandard output
You are given two integers n
and k
along with a string s
.

Your task is to check whether all possible strings of length n
that can be formed using the first k
lowercase English alphabets occur as a subsequence of s
. If the answer is NO, you also need to print a string of length n
that can be formed using the first k
lowercase English alphabets which does not occur as a subsequence of s
.

If there are multiple answers, you may print any of them.

Note: A string a
is called a subsequence of another string b
if a
can be obtained by deleting some (possibly zero) characters from b
without changing the order of the remaining characters.