Increasing Subsequences

题目地址：
https://leetcode.com/problems/increasing-subsequences/description/

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:

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.

解题思路：
传统backtracking解法。

代码：

public List<List<Integer>> findSubsequences(int[] nums) {
    Set<List<Integer>> rst= new HashSet<List<Integer>>();
    List<Integer> list = new ArrayList<Integer>();
    findSequence(rst, list, 0, nums);
    List result = new ArrayList(rst);
    return result;
}

public void findSequence(Set<List<Integer>> rst, List<Integer> list, int pos, int[] nums) {
    if (list.size() >= 2) {
        rst.add(new ArrayList(list));
    }
    for (int i = pos; i < nums.length; i++) {
        if(list.size() == 0 || list.get(list.size() - 1) <= nums[i]) {
            list.add(nums[i]);
            findSequence(rst, list, i + 1, nums);
            list.remove(list.size() - 1);
        }
    }
}