1954. Minimum Garden Perimeter to Collect Enough Apples

In a garden represented as an infinite 2D grid, there is an apple tree planted at every integer coordinate. The apple tree planted at an integer coordinate (i, j) has |i| + |j| apples growing on it.

You will buy an axis-aligned square plot of land that is centered at (0, 0).

Given an integer neededApples, return the minimum perimeter of a plot such that at least neededApples apples are inside or on the perimeter of that plot.

The value of |x| is defined as:

• x if x >= 0
• -x if x < 0

class Solution {
public:
    long long minimumPerimeter(long long neededApples) {
        long long res = 1;
        while(neededApples > 0) {
            long long now = ((res * 2 + 1) * (res * 2) / 2 - (res - 1) * (res) / 2 ) * 2 - res;
            now = now * 4 - res * 2 * 4;
            neededApples -= now;
            res++;
        }
        return (res-1) * 8;
    }
};