2609. Find the Longest Balanced Substring of a Binary String

Problem

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'

Solution (Java)

class Solution {
    public int findTheLongestBalancedSubstring(String s) {
        int max = 0;
        for(int i = 0; i < s.length(); ){
            int z = 0, o = 0;
            while(i < s.length() && s.charAt(i) == '0') {
                z++;
                i++;
            }
            while(i < s.length() && s.charAt(i) =='1' && z > o){
                o++;
                i++;
                max = Math.max(max, o*2);
            }
            while(i < s.length() && s.charAt(i) == '1') i++;
        }
        return max;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).