1128. Number of Equivalent Domino Pairs

https://leetcode.com/problems/number-of-equivalent-domino-pairs

Description

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

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