447. Number of Boomerangs

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:2Explanation: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 s = 0;        int sz = points.size();        for(int i = 0; i < sz; ++i){            int x0 = points[i].first;            int y0 = points[i].second;            map<int, int> dis;            for(int j = 0; j < sz; ++j){                int d1 = points[j].first - x0;                int d2 = points[j].second - y0;                int d = d2 * d2 + d1 * d1;                dis[d]++;            }            for(auto itr = dis.begin(); itr != dis.end(); ++itr){               s += (itr->second) * (itr->second - 1);            }            }        return s;    }};