765. Couples Holding Hands

N couples sit in 2N seats arranged in a row and want to hold hands. We want to know the minimum number of swaps so that every couple is sitting side by side. A swap consists of choosing any two people, then they stand up and switch seats.

The people and seats are represented by an integer from 0 to 2N-1, the couples are numbered in order, the first couple being (0, 1), the second couple being (2, 3), and so on with the last couple being (2N-2, 2N-1).

The couples' initial seating is given by row[i] being the value of the person who is initially sitting in the i-th seat.

Example 1:

Input: row = [0, 2, 1, 3]
Output: 1
Explanation: We only need to swap the second (row[1]) and third (row[2]) person.

Example 2:

Input: row = [3, 2, 0, 1]
Output: 0
Explanation: All couples are already seated side by side.

Note:

  1. len(row) is even and in the range of [4, 60].
  2. row is guaranteed to be a permutation of 0...len(row)-1.

Rust Solution

struct Solution;

impl Solution {
    fn min_swaps_couples(mut row: Vec<i32>) -> i32 {
        let n = row.len();
        let mut res = 0;
        for i in 0..n {
            if i % 2 == 1 {
                continue;
            }
            if row[i] == row[i + 1] ^ 1 {
                continue;
            }
            res += 1;
            for j in i + 2..n {
                if row[i] == row[j] ^ 1 {
                    row.swap(i + 1, j);
                    break;
                }
            }
        }
        res
    }
}

#[test]
fn test() {
    let row = vec![0, 2, 1, 3];
    let res = 1;
    assert_eq!(Solution::min_swaps_couples(row), res);
    let row = vec![3, 2, 0, 1];
    let res = 0;
    assert_eq!(Solution::min_swaps_couples(row), res);
}

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