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`