Longest Substring with At Most K Distinct Characters

You are given a string s and an integer m. Your task is to determine the length of the longest contiguous substring of s that contains at most m distinct characters. More formally, if you let F(s, m) denote the desired length, then you must compute:

\( F(s, m) = \max_{[i, j]} \{ j - i + 1 \}\)

subject to the constraint that the substring s[i...j] has at most m distinct characters. It is recommended to use a sliding window algorithm to efficiently solve this problem.

inputFormat

The input is read from standard input (stdin) and has the following format:

• The first line contains an integer t denoting the number of test cases.
• For each test case, there are two lines:
  • The first line contains an integer m (\( m \ge 0 \)).
  • The second line contains the string s. The string will not contain spaces.

Note: If the string is empty or if m is 0, the answer is 0.

outputFormat

For each test case, output a single line containing the length of the longest substring with at most m distinct characters.

The output should be printed to standard output (stdout).

## sample

3
2
abcba
1
aaa
3
aabacbebebe

3
3
7

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