Can anyone suggest me how to solve this problem(https://cses.fi/problemset/task/1087)↵
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You are given a DNA sequence consisting of characters A, C, G, and T.↵
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Your task is to find the shortest DNA sequence that is not a subsequence of the original sequence.↵
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Input↵
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The only input line contains a DNA sequence with n characters.↵
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Output↵
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Print the shortest DNA sequence that is not a subsequence of the original sequence. If there are several solutions, you may print any of them.↵
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Constraints↵
1≤n≤106↵
Example↵
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Input:↵
ACGTACGT↵
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Output:↵
AAA
↵
You are given a DNA sequence consisting of characters A, C, G, and T.↵
↵
Your task is to find the shortest DNA sequence that is not a subsequence of the original sequence.↵
↵
Input↵
↵
The only input line contains a DNA sequence with n characters.↵
↵
Output↵
↵
Print the shortest DNA sequence that is not a subsequence of the original sequence. If there are several solutions, you may print any of them.↵
↵
Constraints↵
1≤n≤106↵
Example↵
↵
Input:↵
ACGTACGT↵
↵
Output:↵
AAA