Count binary substrings

Two Pointers String

70.3% acceptance

Feb 20, 2026

4631

972

Given a binary string s, return the number of non-empty substrings that have equal numbers of 0's and 1's grouped consecutively.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn count_binary_substrings(s: String) -> i32 {
    let s = s.as_bytes();
    let mut result = 0;
    let mut prev = 0;
    let mut cur = 1;
    for i in 1..s.len() {
      if s[i] == s[i - 1] {
        cur += 1;
      } else {
        prev = cur;
        cur = 1;
      }
      if prev >= cur {
        result += 1;
      }
    }
    result
  }
}