Minimum domino rotations for equal row

Array Greedy

56.5% acceptance

Feb 25, 2026

3284

271

In a row of dominoes, tops[i] and bottoms[i] represent the top and bottom halves of the ith domino. (A domino is a tile with two numbers from 1 to 6 - one on each half of the tile.) We may rotate the ith domino, so that tops[i] and bottoms[i] swap values. Return the minimum number of rotations so that all the values in tops are the same, or all the values in bottoms are the same. If it cannot be done, return -1.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn min_domino_rotations(tops: Vec<i32>, bottoms: Vec<i32>) -> i32 {
    let n = tops.len();
    let try_val = |v: i32| -> i32 {
      let (mut rt, mut rb) = (0i32, 0i32);
      for i in 0..n {
        if tops[i] != v && bottoms[i] != v { return i32::MAX; }
        else if tops[i] != v { rt += 1; }
        else if bottoms[i] != v { rb += 1; }
      }
      rt.min(rb)
    };
    let ans = [try_val(tops[0]), try_val(bottoms[0])].into_iter().min().unwrap();
    if ans == i32::MAX { -1 } else { ans }
  }
}