# Number of Equivalent Domino Pairs

Easy

1

40.0% 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

- Export the function
`numEquivDominoPairs`

from`index.js`

. - Implement the function
`numEquivDominoPairs`

such that it passes the given test cases and any additional tested cases.