LeetCode 1234: Replace the Substring for Balanced String Solution

Master LeetCode problem 1234 (Replace the Substring for Balanced String), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1234. Replace the Substring for Balanced String

Medium

String Sliding Window

Problem Explanation

Explanation

To solve this problem, we can use a sliding window approach. We first calculate the frequency of each character in the given string s. Then, we iterate through the string with a window of size n/4 and keep track of the excess characters that need to be replaced to balance the string. We move the window to find the minimum length of the substring that needs to be replaced.

Calculate the frequency of each character in the string.
Initialize the window with the size n/4 and count the excess characters.
Slide the window to find the minimum length.
Update the window and count the excess characters until we find the minimum length.

Time Complexity: O(n) where n is the length of the input string s.
Space Complexity: O(1)

Solution Code

class Solution {
    public int balancedString(String s) {
        int n = s.length();
        int[] freq = new int[128];
        int count = n / 4;

        for (char c : s.toCharArray()) {
            freq[c]++;
        }

        int start = 0, minLen = n;
        for (int end = 0; end < n; end++) {
            freq[s.charAt(end)]--;

            while (start < n && freq['Q'] <= count && freq['W'] <= count && freq['E'] <= count && freq['R'] <= count) {
                minLen = Math.min(minLen, end - start + 1);
                freq[s.charAt(start)]++;
                start++;
            }
        }

        return minLen;
    }
}

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