LeetCode 356. Line Reflection

very straight forward.

#include <vector>
#include <iostream>
using namespace std;

/*
  Given n points on a 2D plane and find if there is such a line parallel to y-axis that reflect the given set of points.
  Example:
  Given points = [[1, 1], [-1,  1]] return true;
  Given points = [[1, 1], [-1, -1]] return false;
*/

/*
  Think that, if all points are reflect each other. We need to first find the line. The line should be in the middle of (min, max).
  For other points, if two point reflect, the y-ith should be same, (min, max) / 2 - x1 = (min, max) / 2 - x2.
*/
bool isReflected(vector< pair<int, int> >& points) {
  unordered_map< int, set<int> > m;
  int minX = INT_MAX, maxX = INT_MIN;
  for(int i = 0; i < points.size(); ++i) {
    minX = min(points[i].first, minX);
    maxX = max(points[i].first, maxX);
    m[points[i].first].insert(points[i].second);
  }
  double y = double(maxX + minX) / 2;
  for(int i = 0; i < points.size(); ++i) {
    int t = 2*y - points[i].first;
    if(!m.count(t) || !m[t].count(points[i].second)) return false;
  }
  return true;
}

// second method
bool isReflectedII(vector<pair<int, int> >& points) {
  if(point.size() == 0) return true;
  set< pair<int, int> > res;
  double y = 0;
  for(auto a : points) {
    res.insert(a);
    y += a.first;
  }
  y = y / points.size();
  for(auto a : res) {
    if(!res.count((2 * y - a.first), a.second)) return false;
  }
  return true;
}