You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times.

Return the length of the longest substring containing the same letter you can get after performing the above operations.

Example 1:

Input: s = "ABAB", k = 2
Output: 4
Explanation: Replace the two 'A's with two 'B's or vice versa.

Example 2:

Input: s = "AABABBA", k = 1
Output: 4
Explanation: Replace the one 'A' in the middle with 'B' and form "AABBBBA".
The substring "BBBB" has the longest repeating letters, which is 4.

Generate all substrings

    abc
    --
    a
    ab
    abc
    b
    bc
    c

Use HashMap to count the number of characters in each substring

    banana
    ------
    b -> 1
    a -> 3
    n -> 2

    The maximum number of characters is 'a' => 3
    len(banana) = 6
    6 - 3 = 3 
    The number of changes is 6 - 3 = 3 , k = 3

    Generate all substrings of banana
    The total number of substrings are (6, 1) + (6, 2) + (6, 3) + (6, 4) + (6, 5) + (6, 6) = 2^6 - 1  (no empty string)

    Iterate through all substrings and find the maximum of character count

    ana
    a -> 2
    n -> 1

    m = len(ana) - 2 = 1
    if (m == k)
    then get the length of ana which is 3

Source Code

    $b/java/LongestRepeatingCharRep.java