You are given a string s of length n containing only four kinds of characters: 'Q', 'W', 'E', and 'R'.
A string is said to be balanced if each of its characters appears n / 4 times where n is the length of the string.
Return the minimum length of the substring that can be replaced with any other string of the same length to make s balanced. If s is already balanced, return 0.
Example 1:
Input: s = "QWER" Output: 0 Explanation: s is already balanced.
Example 2:
Input: s = "QQWE" Output: 1 Explanation: We need to replace a 'Q' to 'R', so that "RQWE" (or "QRWE") is balanced.
Example 3:
Input: s = "QQQW" Output: 2 Explanation: We can replace the first "QQ" to "ER".
Constraints:
n == s.length4 <= n <= 105n is a multiple of 4.s contains only 'Q', 'W', 'E', and 'R'.The sliding window technique is ideal for problems involving substrings or adding elements to arrays incrementally. Here, we'll form a window which slides over the string until each possible character's frequency is less than or equal to n/4, starting from the beginning of the string and moving rightwards.
This function seeks the shortest substring such that replacing it makes other frequencies balanced. It uses character counting and string manipulation, applying a sliding window to reduce the space of search efficiently.
C++
Java
Python
C#
JavaScript
Time Complexity: O(n), as every index is visited at most twice.
Space Complexity: O(1), as the addition of auxiliary storage is constant.
This approach increases string traversal efficiency by using two pointers to monitor segment boundaries, overflowing initially until satisfied by frequency and effectively reducing substring lengths by adjusting inward.
The C code implements a two-pointer technique with an initial frequency count for excess characters, tuning explicitly within the string length constraints.
C++
Java
Python
C#
JavaScript
Time Complexity: O(n)
Space Complexity: O(1)
| Approach | Complexity |
|---|---|
| Sliding Window Approach | Time Complexity: O(n), as every index is visited at most twice. |
| Two-Pointer Technique | Time Complexity: O(n) |
Longest Repeating Character Replacement - Leetcode 424 - Python • NeetCode • 599,364 views views
Watch 9 more video solutions →Practice Replace the Substring for Balanced String with our built-in code editor and test cases.
Practice on FleetCodePractice this problem
Open in Editor