2609

2609. Find the Longest Balanced Substring of a Binary String (Easy)

You are given a binary string s consisting only of zeroes and ones.

A substring of s is considered balanced if all zeroes are before ones and the number of zeroes is equal to the number of ones inside the substring. Notice that the empty substring is considered a balanced substring.

Return the length of the longest balanced substring of s.

A substring is a contiguous sequence of characters within a string.

 

Example 1:

Input: s = "01000111"
Output: 6
Explanation: The longest balanced substring is "000111", which has length 6.

Example 2:

Input: s = "00111"
Output: 4
Explanation: The longest balanced substring is "0011", which has length 4. 

Example 3:

Input: s = "111"
Output: 0
Explanation: There is no balanced substring except the empty substring, so the answer is 0.

 

Constraints:

• 1 <= s.length <= 50
• '0' <= s[i] <= '1'

Related Topics:
String

Solution 1.

// OJ: https://leetcode.com/problems/find-the-longest-balanced-substring-of-a-binary-string
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int findTheLongestBalancedSubstring(string s) {
        int N = s.size(), i = 0, ans = 0;
        while (i < N) {
            int zero = 0, one = 0;
            while (i < N && s[i] == '0') ++i, ++zero;
            while (i < N && s[i] == '1') ++i, ++one;
            ans = max(ans, min(zero, one) * 2);
        }
        return ans;
    }
};