leetcode-master/problems/0046.全排列.md

## 题目地址 
https://leetcode-cn.com/problems/permutations/

## 思路 

先写逻辑，再确认参数，先把for循环写出来，在写 结束语句，在写 函数参数。

这道题目树形结构还不太一样

## 解法 

```
class Solution {
public:
    vector<vector<int>> result;
    void backtracking (vector<int>& nums, vector<int>& vec, vector<bool>& used) {
        // 此时说明找到了一组
        if (vec.size() == nums.size()) {
            result.push_back(vec);
            return;
        }

        for (int i = 0; i < nums.size(); i++) {
            if (used[i] == false) {
                used[i] = true;
                vec.push_back(nums[i]);
                backtracking(nums, vec, used);
                vec.pop_back();
                used[i] = false;
            }
        }
    }
    vector<vector<int>> permute(vector<int>& nums) {
        vector<bool> used(nums.size(), false);
        vector<int> vec;
        backtracking(nums, vec, used);
        return result;
    }
};
```

这是一个思路：
class Solution {
public:
    vector<vector<int>> res;
    vector<vector<int>> permute(vector<int>& nums) {
        solve(nums, 0);
        return res;
    }
    void solve(vector<int> &nums, int idx) {
        if(idx == nums.size()-1 || nums.size() == 0){
            res.push_back(nums);
            return;
        }
        for(int i = idx; i < nums.size(); i++){
            swap(nums[idx], nums[i]);
            solve(nums, idx+1);
            swap(nums[idx], nums[i]);
        }
    }
};