447.cpp

// hashmap+beat97%.cpp
class Solution {
public:
  int numberOfBoomerangs(vector<pair<int, int>> &points) {
    int n = points.size(), count = 0;
    unordered_map<int, int> map;
    for (int i = 0; i < n; ++i) {
      for (int j = 0; j < n; ++j) {
        if (j == i)
          continue;
        map[dist(points[i], points[j])]++;
      }
      for (auto it = map.begin(); it != map.end(); ++it)
        count += (it->second) * (it->second - 1);
      map.clear();
    }
    return count;
  }
  int dist(pair<int, int> &i, pair<int, int> &j) {
    int x = i.first - j.first;
    int y = i.second - j.second;
    return x * x + y * y;
  }
};
// TLE.cpp
class Solution2 {
public:
  int numberOfBoomerangs(vector<pair<int, int>> &points) {
    int n = points.size(), count = 0;
    for (int i = 0; i < n; ++i)
      for (int j = 0; j < n; ++j)
        if (j == i)
          continue;
        else
          for (int k = 0; k < n; ++k)
            if (k == i || k == j)
              continue;
            else if (dist(i, j, points) == dist(i, k, points))
              count++;
    return count;
  }
  int dist(int i, int j, vector<pair<int, int>> &points) {
    int x = points[i].first - points[j].first;
    int y = points[i].second - points[j].second;
    return x * x + y * y;
  }
};