491. Increasing Subsequences

Given an integer array, your task is to find all the different possible increasing subsequences of the given array, and the length of an increasing subsequence should be at least 2 .

Example:

Input: [4, 6, 7, 7]Output: [[4, 6], [4, 7], [4, 6, 7], [4, 6, 7, 7], [6, 7], [6, 7, 7], [7,7], [4,7,7]]

Note:

1. The length of the given array will not exceed 15.
2. The range of integer in the given array is [-100,100].
3. The given array may contain duplicates, and two equal integers should also be considered as a special case of increasing sequence.

原本的想法是从原数组减去一个数，但这样就不符合增序的要求。所以反过来，从单个数往上加，加的时候判断一下是否符合条件。

public class Solution {    public List<List<Integer>> findSubsequences(int[] nums) {        Set<List<Integer>> set=new HashSet<>();        LinkedList<Integer> hold=new LinkedList<>();        helper(hold,set,nums,0);        List res=new ArrayList(set);        return res;    }    public void helper(LinkedList<Integer> hold, Set<List<Integer>> set,int[] nums ,int index){        if(hold.size()>=2)            set.add(new LinkedList<>(hold));        for(int i=index;i<nums.length;i++){            if(hold.size()==0||hold.get(hold.size()-1)<=nums[i]){                hold.add(nums[i]);                helper(hold,set,nums,i+1);                hold.remove(hold.size()-1);            }        }    }}