leetcode 279: Perfect Squares

Perfect Squares

Total Accepted: 605 Total Submissions: 1956

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.

[思路]

离散背包问题, 用DP解决.

[CODE]

public class Solution {
    public int numSquares(int n) {
        int[] d = new int[n+1];
        d[1] = 1;
        
        for(int i=2; i<=n; i++) {
            int min = Integer.MAX_VALUE;
            int j=1;
            while(j*j<=i) {
                if(j*j==i) {
                    min = 1; break;
                }
                min = Math.min(min, d[i-j*j]+1);
                ++j;
            }
            d[i] = min;
        }
        return d[n];
    }
}