Leetcode 279. Perfect Squares

问题描述

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.

问题分析：
把target分成两个数，然后分别两个数的最少平方和的数目相加即为target的最少平和的数目。
代码如下：

    public int numSquares(int n) {        if(n<=0)            return 0;        int[]dp=new int[n+1];        dp[0]=0;        dp[1]=1;        int index=2;        for(int i=2;i<=n;i++){            if(i==index*index)            {                dp[i]=1;                index++;            }                else{                dp[i]=Integer.MAX_VALUE;                for(int j=1;j<=i/2;j++){                    dp[i]=Math.min(dp[i],dp[j]+dp[i-j]);                }            }        }        return dp[n];    }