Alternating groups i

Array Sliding Window

68.8% acceptance

Feb 25, 2026

169

There is a circle of red and blue tiles. You are given an array of integers colors. The color of tile i is represented by colors[i]: colors[i] == 0 means that tile i is red. colors[i] == 1 means that tile i is blue. Every 3 contiguous tiles in the circle with alternating colors (the middle tile has a different color from its left and right tiles) is called an alternating group. Return the number of alternating groups. Note that since colors represents a circle, the first and the last tiles are considered to be next to each other.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn number_of_alternating_groups(colors: Vec<i32>) -> i32 {
    let n = colors.len();
    let mut count = 0;
    for i in 0..n {
      if colors[i] != colors[(i + 1) % n] && colors[(i + 1) % n] != colors[(i + 2) % n] {
        count += 1;
      }
    }
    count
  }
}