README.md

2609. Find the Longest Balanced Substring of a Binary String

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'

Solutions (Rust)

1. Solution

impl Solution {
    pub fn find_the_longest_balanced_substring(s: String) -> i32 {
        let s = s.as_bytes();
        let mut count0 = (b'1' - s[0]) as i32;
        let mut count1 = 0;
        let mut ret = 0;

        for i in 1..s.len() {
            if s[i] == b'0' && s[i - 1] == b'1' {
                count0 = 0;
                count1 = 0;
            }

            if s[i] == b'0' {
                count0 += 1;
            } else if s[i] == b'1' {
                count1 += 1;
            }

            ret = ret.max(count0.min(count1) * 2);
        }

        ret
    }
}