代码随想录算法训练营第二十五天|491 递增子序列、46 全排列、47 全排列||

一、491 递增子序列

class Solution {
private:
    vector<vector<int>>result;
    vector<int>path;
    void backtracking(vector<int>& nums,int startindex){
        if(path.size()>1)
            result.push_back(path);
        unordered_set<int> uset;
        for(int i=startindex;i<nums.size();i++){
            if(!path.empty()&&nums[i]<path.back()||uset.find(nums[i])!=uset.end())
                continue;
            uset.insert(nums[i]);
            path.push_back(nums[i]);
            backtracking(nums,i+1);
            path.pop_back();
            //uset不用回溯，因为每递归一次就会创建一个新的uset
        }
    }
public:
    vector<vector<int>> findSubsequences(vector<int>& nums) {
        backtracking(nums,0);
        return result;
    }
};

二、46 全排列

class Solution {
private:
    vector<vector<int>>result;
    vector<int>path;
    void backtracking(vector<int>& nums,vector<bool>&used){
            if(path.size() == nums.size()){
                result.push_back(path);
                return;
            }
            for(int i=0;i<nums.size();i++){
                if(used[i]==true)
                    continue;
                path.push_back(nums[i]);
                used[i] = true;
                backtracking(nums,used);
                path.pop_back();
                used[i] = false;
            }
    }
public:
    vector<vector<int>> permute(vector<int>& nums) {
        vector<bool>used(nums.size(),false);
        backtracking(nums,used);
        return result;
    }
};

三、47 全排列||

class Solution {
private:
    vector<vector<int>>result;
    vector<int>path;
    void backtracking(vector<int>& nums,vector<bool>&used){
        if(path.size()==nums.size()){
            result.push_back(path);
            return;
        }
        for(int i=0;i<nums.size();i++){
            if(i>0&&nums[i]==nums[i-1]&&used[i-1]==false)
                continue;
            if(used[i]==false){
                used[i] = true;
            path.push_back(nums[i]);
            backtracking(nums,used);
            path.pop_back();
            used[i] = false;
            }
        }
    }
public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        vector<bool>used(nums.size(),false);
        sort(nums.begin(),nums.end());
        backtracking(nums,used);
        return result;
    }
};