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 because12 = 4 + 4 + 4; given n = 13, return 2 because13 = 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];    }};