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.

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

动态规划。

class Solution {
    public int numSquares(int n) {
        int[] dp = new int[n+1];
        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];
    }
}