leetcode题解Java | 491. Increasing Subsequences

题目：

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:

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

用递归的方式暴力搜索。从当前节点起往后找比自己大的点，找到了，就存起来，然后进入下一层递归。注意，我第一次提交的时候TLE了，然后看了下排名第一的solution，说是beat100%，竟然和我写的一模一样，后来又交了一次，过了，但只beat了20%左右。

Java实现：

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