> For the complete documentation index, see [llms.txt](https://dfine.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dfine.gitbook.io/leetcode/46.permutations.md).

# 46.Permutations

**46.Permutations**

难度:Medium

> Given a collection of distinct integers, return all possible permutations.

Example:

```
Input: [1,2,3]
Output:
[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]
```

采用回溯法，想将每一位放在第一位，然后对于剩下的，将每一位放在第二位，一直循环下去。

```
class Solution {
vector<vector<int>>res;
void traceback(int n, int step)
{
    if(step == n) return;
    int len=res.size();
    for(int i=0;i<len;i++)
    {
        for(int j=step+1;j<n;j++)
        {
            vector<int> tmp(res[i]);
        swap(res[i][step],res[i][j]);
        res.push_back(tmp);
        }
    }
    traceback(n,step+1);
}
public:
    vector<vector<int>> permute(vector<int>& nums) {
        res.push_back(nums);
        traceback(nums.size(), 0);
        return res;
    }
};
```

> 执行用时 :12 ms, 在所有 C++ 提交中击败了98.71%的用户\
> 内存消耗 :9.7 MB, 在所有 C++ 提交中击败了29.71%的用户


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