算法训练day31 LeetCode 491.46.47.

491.递增子序列

题目

491. 递增子序列 - 力扣（LeetCode）

题解

代码随想录 (programmercarl.com)

递增子序列，意味着不能改变数组中元素顺序

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> used;
        for (int i = startIndex; i < nums.size(); i++)
        {
            if ((!path.empty() && nums[i] < path.back()) || used.find(nums[i]) != used.end())
            {
                continue;
            }
            used.insert(nums[i]);
            path.push_back(nums[i]);
            backtracking(nums, i + 1);
            path.pop_back();
        }
    }

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

46.全排列

题目

46. 全排列 - 力扣（LeetCode）

题解

代码随想录 (programmercarl.com)

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; // path已收录，跳过
            used[i] = true;
            path.push_back(nums[i]);
            backtracking(nums, used);
            path.pop_back();
            used[i] = false;
        }
    }
    vector<vector<int>> permute(vector<int> &nums)
    {
        result.clear();
        path.clear();
        vector<bool> used(nums.size(), false);
        backtracking(nums, used);
        return result;
    }
};

47.全排列 II

题目

47. 全排列 II - 力扣（LeetCode）

题解

代码随想录 (programmercarl.com)

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