Perfect Squares

Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.

For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9.

class Solution {
public:
    int numSquares(int n) {
        vector<int> buf(n+1, INT_MAX-1);
        
        buf[0] = 0;
        buf[1] = 1;
        for (int i = 2; i <= n; i++)
        {
            for (int j = 1; j*j <= i; j++)
            {
                buf[i] = min(buf[i], buf[i-j*j]+1);
            }
        }

        return buf[n];
    }
};