README.md

1128. Number of Equivalent Domino Pairs

Given a list of dominoes, dominoes[i] = [a, b] is equivalent to dominoes[j] = [c, d] if and only if either (a==c and b==d), or (a==d and b==c) - that is, one domino can be rotated to be equal to another domino.

Return the number of pairs (i, j) for which 0 <= i < j < dominoes.length, and dominoes[i] is equivalent to dominoes[j].

Example 1:

Input: dominoes = [[1,2],[2,1],[3,4],[5,6]]
Output: 1

Constraints:

• 1 <= dominoes.length <= 40000
• 1 <= dominoes[i][j] <= 9

Solutions (Rust)

1. Count

impl Solution {
    pub fn num_equiv_domino_pairs(dominoes: Vec<Vec<i32>>) -> i32 {
        let mut cnt = [0; 100];
        let mut ret = 0;
        for domino in dominoes {
            let tens = domino[0].min(domino[1]) as usize;
            let units = domino[0].max(domino[1]) as usize;
            ret += cnt[tens * 10 + units];
            cnt[tens * 10 + units] += 1;
        }
        ret
    }
}