1227 Number Of Equivalent Domino Pairs

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

Example 2:

**Input:** dominoes = [[1,2],[1,2],[1,1],[1,2],[2,2]]
**Output:** 3

 

Constraints:

1 <= dominoes.length <= 4 * 104
dominoes[i].length == 2
1 <= dominoes[i][j] <= 9

use std::collections::HashMap ;
use std::cmp::max;

impl Solution {
    pub fn num_equiv_domino_pairs(dominoes: Vec<Vec<i32>>) -> i32 {
        let mut mp = HashMap::new();
        for k in dominoes {
            if k[0] > k[1] {
                let state = mp.entry((k[1], k[0])).or_insert(0);
                *state += 1;

            } else {
                let state = mp.entry((k[0], k[1])).or_insert(0);
                *state += 1;
            }
            
        }
        let mut res = 0;
        for (k,v) in mp {
            if v > 1 {
                res += v * (v-1) / 2;
            }
        }
        return res 
    }
}