题目

代码如下：

class Solution {
public:
vector<vector<int>> res;
vector<int> path;
bool occured(vector<int>& nums, int key, int startindex){
    for(int i = startindex; i < key; i++){
        if(nums[key] == nums[i]){
            return true;
        }
    }
    return false;
}
void backtrace(vector<int>& nums, int startindex, int length){
    if(length >= 2 && path.size() == length){
        //去重
        res.push_back(path);
    }
    if(startindex >= nums.size()){
        //控制子序列为非递减
        return ;
    }

    for(int i = startindex; i < nums.size(); i++){
        if(i != startindex && occured(nums, i,startindex)){
           continue;
        }
        if(nums[i] < path.back()){
            continue;
        }
        path.push_back(nums[i]);
        backtrace(nums, i+1, length+1);
        path.pop_back();
    }
}
    vector<vector<int>> findSubsequences(vector<int>& nums) {
        res.clear();
        path.clear();
        for(int i = 0; i < nums.size(); i++){
            //先在path中遍历第一个元素
            //这一步写在backtrace里的话会很不好处理
            if(i != 0 && occured(nums, i,0)){
                continue;
            }
            path.push_back(nums[i]);
            backtrace(nums,i+1, 1);
            path.pop_back();
        }
        return res;
    }
};

如果把对path第一个元素的处理也写在backtrace里的话：

没写出来，不写了