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 min(int a, int b)    {        if(a < b)            return a;        return b;    }    int numSquares(int n)    {        vector<int> vec(n + 1, 0);        for(int i = 1; i * i <= n; ++i)        {            vec[i * i] = 1;        }        for(int i = 1; i <= n; ++i)        {            for(int j = 1; i + j*j <= n; ++j)            {                if(vec[i + j * j] != 0)                    vec[i + j * j] = min(vec[i + j * j], vec[i] + 1);                else                    vec[i + j * j] = vec[i] + 1;            }        }        return vec[n];    }};