447.md

447. Number of Boomerangs

Description

Given n points in the plane that are all pairwise distinct, 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).

Find the number of boomerangs. You may assume that n will be at most 500 and coordinates of points are all in the range [-10000, 10000] (inclusive).

Example:

Input:
[[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]]

Solution

/**
 * Iterate through ES6 Map is way more faster than iterate through Object
 * Ref: https://jsperf.com/es6-map-vs-object-properties/2
 * @param {number[][]} points
 * @return {number}
 */
var numberOfBoomerangs = function(points) {
    "use strict";
    function calDist(pointA, pointB) {
        return Math.pow(pointA[0]-pointB[0], 2) + Math.pow(pointA[1]-pointB[1], 2);
    }
    let result = 0;
    for (let i = 0; i < points.length; i++) {
        let map = new Map();
        for (let j = 0; j < points.length; j++) {
            if (i === j) {
                continue;
            }
            let dist = calDist(points[i], points[j]);
            if (map.get(dist) === undefined) {
                map.set(dist, 0);
            }
            map.set(dist, map.get(dist)+1);
        }
        map.forEach((item) => result += item * (item-1));
    }
    return result;
};