完全平方数问题

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.


方法1: 看作是01背包问题，用动态规划解决

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