279. 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.

public class Solution {    public int numSquares(int n) {        int[] dp = new int[n+1];        Arrays.fill(dp, Integer.MAX_VALUE);        dp[0] = 0;        for (int i = 1; i <= n; i++) {            int min = Integer.MAX_VALUE;            int j = 1;            while (j * j <= i) {                min = Math.min(min, 1+dp[i-j*j]);                j++;            }            dp[i] = min;        }        return dp[n];    }}