Perfect Squares——Leetcode

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

.

题目大意：给一个正整数，找出可以由最少个平方数构成的数量是多少。

解题思路：dynamic programming，递推公式F
=min{F[n-1]+1,F[n-4]+2,F[n-9]+3,...};

public class Solution {
int[] f;
public int numSquares(int n) {
f=new int[n+1];
Arrays.fill(f,Integer.MAX_VALUE);
f[1]=1;
for(int i=2;i<=n;i++){
int r = (int)Math.sqrt(i);
if(i==r*r){
f[i]=1;
continue;
}
for(int j=1;j<=r;j++){
f[i]=Math.min(f[i],f[i-j*j]+1);
}
}
return f
;
}
}