# Number of Equivalent Domino Pairs

Easy
1
50.0% Acceptance

In this lab, you will build a function that calculates the number of equivalent domino pairs. A pair 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`). In other words, one domino can be rotated to be equal to another domino.

Your task is to create a function `numEquivDominoPairs` that takes an array of dominoes as input and returns the number of equivalent pairs `(i, j)` for which `0 <= i < j < dominoes.length` and `dominoes[i]` is equivalent to `dominoes[j]`.

Example 1:

``````const dominoes = [
[1, 2],
[2, 1],
[3, 4],
[5, 6],
];
console.log(numEquivDominoPairs(dominoes)); // Output: 1``````

Example 2:

``````const dominoes = [
[1, 2],
[1, 2],
[1, 1],
[1, 2],
[2, 2],
];
console.log(numEquivDominoPairs(dominoes)); // Output: 3``````

Constraints:

• `1 <= dominoes.length <= 4 * 104`
• `dominoes[i].length == 2`
• `1 <= dominoes[i][j] <= 9`

## Challenges

1. Export the function `numEquivDominoPairs` from `index.js`.
2. Implement the function `numEquivDominoPairs` such that it passes the given test cases and any additional tested cases.