LeetCode 1128. Number of Equivalent Domino Pairs

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class Solution {
public:
    int numEquivDominoPairs(vector<vector<int>>& dominoes) {
        vector<int> numCnt(100, 0);
        int ans = 0;
        for (const auto& d : dominoes) {
            int v = d[0] < d[1] ? d[0] * 10 + d[1] : d[1] * 10 + d[0];
            ans += numCnt[v];
            ++numCnt[v];
        }
        return ans;
    }
};