491.递增子序列

力扣题目链接

vector<vector<int>> result;
    vector<int> path;

    void backtracking1(vector<int>& nums, int startIndex) {
        // size小于2的结果不加入
        if (path.size() > 1) {
            result.push_back(path);
            // 注意此处不return，因为要取树上的节点
        }
        unordered_set<int> uset;
        for (int i = startIndex; i < nums.size(); ++i) {
            // 注意此处的筛选逻辑
            if ((!path.empty() && nums[i] < path.back()) || uset.find(nums[i]) != uset.end()) {
                continue;
            }
            uset.insert(nums[i]);
            path.push_back(nums[i]);
            backtracking1(nums, i + 1);
            path.pop_back();
        }
    }

    // 使用数组哈希替代unordered_set
    void backtracking(vector<int>& nums, int startIndex) {
        if (path.size() > 1) {
            result.push_back(path);
        }
        // 哈希数组的取值范围[-100, 100] 201个标志位
        int used[201] = {0};
        for (int i = startIndex; i < nums.size(); ++i) {
            if ((!path.empty() && nums[i] < path.back()) || used[nums[i] + 100] == 1) {
                continue;
            }
            used[nums[i] + 100] = 1;
            path.push_back(nums[i]);
            backtracking(nums, i + 1);
            path.pop_back();
        }
    }

    vector<vector<int>> findSubsequences(vector<int>& nums) {
        result.clear();
        path.clear();
        backtracking(nums, 0);
        return result;
    }

46.全排列

力扣题目链接

// 时间复杂度: O(n!)
// 空间复杂度: O(n)

    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) {
        path.clear();
        result.clear();
        vector<bool> used(nums.size(), false);
        backtracking(nums, used);
        return result;
    }

47.全排列 II

力扣题目链接

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;
            }
        }
    }
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        result.clear();
        path.clear();
        sort(nums.begin(), nums.end());
        vector<bool> used(nums.size(), false);
        backtracking(nums, used);
        return result;
    }