Minimum changes to make alternating binary string

String

63.8% acceptance

Feb 25, 2026

1500

You are given a string s consisting only of the characters '0' and '1'. In one operation, you can change any '0' to '1' or vice versa. The string is called alternating if no two adjacent characters are equal. For example, the string "010" is alternating, while the string "0100" is not. Return the minimum number of operations needed to make s alternating.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn min_operations(s: String) -> i32 {
    // Count mismatches with "010101..." pattern
    let cost1 = s.bytes().enumerate()
      .filter(|&(i, c)| c - b'0' != (i % 2) as u8)
      .count() as i32;
    // Mismatches with "101010..." = n - cost1
    cost1.min(s.len() as i32 - cost1)
  }
}