973. K Closest Points to Origin

Given an array of points where points[i] = [xi, yi] represents a point on the X-Y plane and an integer k, return the k closest points to the origin (0, 0).

The distance between two points on the X-Y plane is the Euclidean distance (i.e., √(x1 - x2)2 + (y1 - y2)2).

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

class Solution {
public:
    vector<vector<int>> kClosest(vector<vector<int>>& points, int k) {
        sort(begin(points), end(points), [](const vector<int>& a, const vector<int>& b) { return a.front() * a.front() + a.back() * a.back() < b.front() * b.front() + b.back() * b.back(); });
        return vector<vector<int>> (points.begin(), points.begin() + k);
    }
};