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'