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# 0447. Number of Boomerangs

<https://leetcode.com/problems/number-of-boomerangs>

## Description

You are given `n` `points` in the plane that are all **distinct**, where `points[i] = [xi, yi]`. A **boomerang** is a tuple of points `(i, j, k)` such that the distance between `i` and `j` equals the distance between `i` and `k` **(the order of the tuple matters)**.

Return *the number of boomerangs*.

**Example 1:**

```
**Input:** points = [[0,0],[1,0],[2,0]]
**Output:** 2
**Explanation:** The two boomerangs are [[1,0],[0,0],[2,0]] and [[1,0],[2,0],[0,0]].
```

**Example 2:**

```
**Input:** points = [[1,1],[2,2],[3,3]]
**Output:** 2
```

**Example 3:**

```
**Input:** points = [[1,1]]
**Output:** 0
```

**Constraints:**

* `n == points.length`
* `1 <= n <= 500`
* `points[i].length == 2`
* `-104 <= xi, yi <= 104`
* All the points are **unique**.

## ac

```java
```