LeetCode-973. K Closest Points to Origin

We have a list of ​​points​​​ on the plane.  Find the ​​K​​​ closest points to the origin ​​(0, 0)​​.

(Here, the distance between two points on a plane is the Euclidean distance.)

You may return the answer in any order.  The answer is guaranteed to be unique (except for the order that it is in.)

 

Example 1:

Input: points = [[1,3],[-2,2]], K = 1
Output: [[-2,2]]
Explanation: 
The distance between (1, 3) and the origin is sqrt(10).
The distance between (-2, 2) and the origin is sqrt(8).
Since sqrt(8) < sqrt(10), (-2, 2) is closer to the origin.
We only want the closest K = 1 points from the origin, so the answer is just [[-2,2]].

Example 2:

Input: points = [[3,3],[5,-1],[-2,4]], K = 2
Output: [[3,3],[-2,4]]
(The answer [[-2,4],[3,3]] would also be accepted.)

 

Note:

1. ​​1 <= K <= points.length <= 10000​​
2. ​​-10000 < points[i][0] < 10000​​
3. ​​-10000 < points[i][1] < 10000​​

​​题解：​​

class Solution {
public:
  static bool cmp (pair<int, int> a, pair<int, int> b) {
    return a.second < b.second;
  }
  vector<vector<int>> kClosest(vector<vector<int>>& points, int K) {
    int n = points.size();
    vector<pair<int, int>> vm;
    vector<vector<int>> ans;
    for (int i = 0; i < n; i++) {
      vm.push_back(make_pair(i, points[i][0] * points[i][0] + points[i][1] * points[i][1]));
    }
    sort(vm.begin(), vm.end(), cmp);
    for (int i = 0; i < K; i++) {
      ans.push_back(points[vm[i].first]);
    }
    return ans;
  }
};