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 == candb == d, ora == dandb == 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
1Only the dominoes [1, 2] and [2, 1] are equivalent, so there is one valid pair.
Example 2
Input
dominoes = [[1,2],[1,2],[1,1],[1,2],[2,2]]Output
3The three occurrences of [1, 2] are mutually equivalent, forming three valid pairs.
Constraints
- 1 <= dominoes.length <= 4 * 10^4
- dominoes[i].length == 2
- 1 <= dominoes[i][j] <= 9