longest_repeating_character_replacement.py

# https://leetcode.com/problems/longest-repeating-character-replacement/description/
# 424. Longest Repeating Character Replacement

# 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.
# There may exists other ways to achieve this answer too.

# Constraints:
# 1 <= s.length <= 105
# s consists of only uppercase English letters.
# 0 <= k <= s.length

class Solution(object):
    def characterReplacement(self, s: str, k: int) -> int:
        ''' Time Complexity :  O(n) ; Space Complexity : O(1) '''
        counter={}
        res, l = 0, 0
        for r in range(len(s)):
            counter[s[r]] = 1 + counter.get(s[r], 0)
            windowlen = r - l + 1
            maxcount = max(counter.values())
            if (windowlen - maxcount) > k:
                counter[s[l]] -= 1
                l += 1
            res = max(res, r - l + 1)
        return res

# s, k = "AABABBA", 1
# Output: 4
s, k = "AABABBAWORRRPRRR", 1
# Output: 7
Solution().characterReplacement(s, k)