368. Largest Divisible Subset java solutions

Given a set of distinct positive integers, find the largest subset such that every pair (Si, Sj) of elements in this subset satisfies: Si % Sj = 0 or Sj % Si = 0.

If there are multiple solutions, return any subset is fine.

Example 1:

nums: [1,2,3]

Result: [1,2] (of course, [1,3] will also be ok)

Example 2:

nums: [1,2,4,8]

Result: [1,2,4,8]

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

 1 public class Solution {
 2     public List<Integer> largestDivisibleSubset(int[] nums) {
 3         List<Integer> ans = new ArrayList<Integer>();
 4         if( nums.length == 0 || nums == null) return ans;
 5         if(nums.length == 1){
 6             ans.add(nums[0]);
 7             return ans;
 8         }
 9         Arrays.sort(nums);//先将数组排序之后再处理
10         int[] sum = new int[nums.length];
11         int[] pre = new int[nums.length];//能被nums[i]整除的上一个数的索引
12         int max = 0, maxindex = 0;
13         for(int i = 0; i < nums.length; i++){
14             sum[i] = 1;
15             pre[i] = -1;
16             for(int j = 0; j < i; j++){
17                 if(nums[i]%nums[j] == 0){
18                     pre[i] = j;
19                     sum[i] = sum[j] + 1;// nums[i] % nums[j] 则sum[i] = sum[j] + 1
20                     if(sum[i] > max){
21                         max = sum[i];
22                         maxindex = i;
23                     }
24                 }
25             }
26         }
27         while(maxindex != -1){//回溯，依次将数值加入ans
28             ans.add(nums[maxindex]);
29             maxindex = pre[maxindex];
30         }
31         return ans;
32     }
33 }