代码随想录算法训练营第二十八天 | 491.递增子序列 、46.全排列 ，47.全排列 II

491.递增子序列

class Solution {
public:
        vector<vector<int>> result;
        vector<int> path;
        void backtracking(vector<int>& nums, int startIndex) {
            if (path.size() >= 2) {
                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<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; 
            used[i] = true;
            path.push_back(nums[i]);
            backtracking(nums, used);
            path.pop_back();
            used[i] = false;
        }
    }
    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 {
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) {
        sort(nums.begin(), nums.end()); 
        vector<bool> used(nums.size(), false);
        backtracking(nums, used);
        return result;
    }
};