LeetCode #491 - Increasing Subsequences

题目描述：

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.

找出一个数组中所有的单增序列，由于不能改变数组元素顺序，所以比较难进行去重操作，利用集合是比较简单的方法。

class Solution {
public:
    vector<vector<int>> findSubsequences(vector<int>& nums) {
        set<vector<int>> s;
        vector<int> cur;
        findSubsequences_recur(nums,0,cur,s);
        vector<vector<int>> result(s.begin(),s.end());
        return result;
    }
    
    void findSubsequences_recur(vector<int> nums, int i,vector<int> cur, set<vector<int>>& s)
    {
        if(i==nums.size())
        {
            if(cur.size()>=2) s.insert(cur);
            return;
        }
        
        findSubsequences_recur(nums,i+1,cur,s);
        if(cur.size()==0||nums[i]>=cur.back())
        {
            cur.push_back(nums[i]);
            findSubsequences_recur(nums,i+1,cur,s); 
        }
    }
};