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.

Example 1:

Input: n = 12
Output: 3 
Explanation: 12 = 4 + 4 + 4.

Example 2:

Input: n = 13
Output: 2
Explanation: 13 = 4 + 9.

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(i - j * j >= 0) {
                min = Math.min(min, dp[i - j * j] + 1);
                j++;
            }
            dp[i] = min;
        }
        return dp[n];
    }
}

https://leetcode.com/problems/perfect-squares/discuss/71495/An-easy-understanding-DP-solution-in-Java