LeetCode491. Non-decreasing Subsequences

文章目录

• • 一、题目
  • 二、题解

一、题目

Given an integer array nums, return all the different possible non-decreasing subsequences of the given array with at least two elements. You may return the answer in any order.

Example 1:

Input: nums = 4,6,7,7

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

Example 2:

Input: nums = 4,4,3,2,1

Output: \[4,4]

Constraints:

1 <= nums.length <= 15

-100 <= numsi <= 100

二、题解

既可以使用unordered_map进行判断是否在同一层上有重复元素，也可以使用unordered_set进行去重

class Solution {
public:
    vector<int> path;
    vector<vector<int>> res;
    void backtracking(vector<int>& nums,int startIndex){
        if(path.size() > 1) res.push_back(path);
        unordered_map<int,int> map;
        for(int i = startIndex;i < nums.size();i++){
            if((!path.empty() && nums[i] < path.back()) || map[nums[i]] == 1) continue;
            map[nums[i]] = 1;
            path.push_back(nums[i]);
            backtracking(nums,i + 1);
            path.pop_back();
        }
    }
    vector<vector<int>> findSubsequences(vector<int>& nums) {
        backtracking(nums,0);
        return res;
    }
};