# 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`

## ac

```java
```
