[LeetCode] 279. Perfect Squares

Problem

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.

Solution

class Solution {
    public int numSquares(int n) {
        int[] dp = new int[n+1];
        Arrays.fill(dp, n+2);
        dp[0] = 0;
        for (int i = 1; i <= n; i++) {
            int min = dp[i];
            int factor = 1;
            while (i-factor*factor >= 0) {
                min = Math.min(min, dp[i-factor*factor]+1);
                factor++;
            }
            dp[i] = min;
        }
        return dp[n];
    }
}