# 1128. Number of Equivalent Domino Pairs from collections import Counter """ 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'. return the number of pairs '(i, j)' for which '0 <= i < j < dominoes.length' and 'dominoes[i]' is equivalent to 'dominoes[j]'. """ class Solution(object): def numEquivDominoPairs(self, dominoes): """ :type dominoes: List[List[int]] :rtype: int """ return sum( v * (v - 1) / 2 for v in Counter(tuple(sorted(u)) for u in dominoes).values() ) if __name__ == "__main__": obj = Solution() print(obj.numEquivDominoPairs(dominoes=[[1, 2], [2, 1], [3, 4], [5, 6]])) print(obj.numEquivDominoPairs(dominoes=[[1, 2], [1, 2], [1, 1], [1, 2], [2, 2]]))