Leetcode/1128.java at main · chakrabortyrajarshi2005/Leetcode · GitHub

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1128. Number of Equivalent Domino Pairs
DescriptionHintsSubmissionsDiscussSolutions
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


class Solution {

    public int numEquivDominoPairs(int[][] dominoes) {
        int[] num = new int[100];
        int ret = 0;
        for (int[] domino : dominoes) {
            int val = domino[0] < domino[1]
                ? domino[0] * 10 + domino[1]
                : domino[1] * 10 + domino[0];
            ret += num[val];
            num[val]++;
        }
        return ret;
    }
}