LC 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.)

class Solution {
public:
    static bool cmp(vector<long long> a, vector<long long> b){
        return a[2] < b[2];
    }
    vector<vector<int>> kClosest(vector<vector<int>>& points, int K) {
        vector<vector<int>> ret;
        vector<vector<long long>> dist;
        for(auto pv : points) {
            vector<long long> tmp = {pv[0], pv[1], pv[0]*pv[0] + pv[1]*pv[1]};
            dist.push_back(tmp);
        }
        sort(dist.begin(), dist.end(), cmp);
        for(int i=0; i<K; i++){
            vector<int> tmp = {(int)dist[i][0], (int)dist[i][1]};
            ret.push_back(tmp);
        }
        return ret;
    }
};