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.

public class Solution {
    public List<Integer> largestDivisibleSubset(int[] nums) {
        List<Integer> ans = new ArrayList<Integer>();
        if( nums.length == 0 || nums == null) return ans;
        if(nums.length == 1){
            ans.add(nums[0]);
            return ans;
        }
        Arrays.sort(nums);//先将数组排序之后再处理
        int[] sum = new int[nums.length];
        int[] pre = new int[nums.length];//能被nums[i]整除的上一个数的索引
        int max = 0, maxindex = 0;
        for(int i = 0; i < nums.length; i++){
            sum[i] = 1;
            pre[i] = -1;
            for(int j = 0; j < i; j++){
                if(nums[i]%nums[j] == 0){
                    pre[i] = j;
                    sum[i] = sum[j] + 1;// nums[i] % nums[j] 则sum[i] = sum[j] + 1
                    if(sum[i] > max){
                        max = sum[i];
                        maxindex = i;
                    }
                }
            }
        }
        while(maxindex != -1){//回溯，依次将数值加入ans
            ans.add(nums[maxindex]);
            maxindex = pre[maxindex];
        }
        return ans;
    }
}