回溯4

491. 非递减子序列

class Solution {
public:
    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();
        }
    }
    vector<vector<int>> findSubsequences(vector<int>& nums) {
        backTracking(nums, 0);
        return result;
    }
};

46. 全排列

class Solution {
public:
    vector<int> path;
    vector<vector<int>> result;
    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);
            used[i] = false;
            path.pop_back();
        }
    }
    vector<vector<int>> permute(vector<int>& nums) {
        vector<bool> used(nums.size(), false);
        backTracking(nums, used);
        return result;
    }
};

47. 全排列 II

class Solution {
public:
    vector<int> path;
    vector<vector<int>> result;
    void backTracking(vector<int> & nums, vector<bool>& used)
    {
        if(path.size() == nums.size())
        {
            result.push_back(path);
            return;
        }
        unordered_set<int> uset;
        for(int i = 0; i < nums.size(); i++)
        {
            if(used[i] == true || uset.find(nums[i]) != uset.end())
                continue;
            uset.insert(nums[i]);
            used[i] = true;
            path.push_back(nums[i]);
            backTracking(nums, used);
            path.pop_back();
            used[i] = false;
        }
    }
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        vector<bool> used(nums.size(), false);
        backTracking(nums, used);

        return result;
    }
};