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]]
class Solution { public: int numberOfBoomerangs(vector<pair<int, int>>& points) { int num = 0; for (int i = 0; i < points.size(); i++) { unordered_map<long, int> map(points.size()); for (int j = 0; j < points.size(); j++) { if (i == j) continue; int dx = points[i].first - points[j].first; int dy = points[i].second - points[j].second; long key = dx*dx + dy*dy; map[key]++; } for (auto& a : map) { if (a.second > 1) { num += a.second * (a.second-1); } } } return num; } };