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.

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