# 0046. Permutations

<https://leetcode.com/problems/permutations>

## Description

Given an array `nums` of distinct integers, return *all the possible permutations*. You can return the answer in **any order**.

**Example 1:**

```
**Input:** nums = [1,2,3]
**Output:** [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
```

**Example 2:**

```
**Input:** nums = [0,1]
**Output:** [[0,1],[1,0]]
```

**Example 3:**

```
**Input:** nums = [1]
**Output:** [[1]]
```

**Constraints:**

* `1 <= nums.length <= 6`
* `-10 <= nums[i] <= 10`
* All the integers of `nums` are **unique**.

## ac

```java
class Solution {
    public List<List<Integer>> permute(int[] nums) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        backtrack(nums, nums.length, res, new ArrayList<Integer>(), new boolean[nums.length]);
        return res;
    }

    private void backtrack(int[] nums, int remain, List<List<Integer>> res, List<Integer> note, boolean[] visiting) {
        // exit
        if (remain == 0) {
            res.add(new ArrayList<Integer>(note));
            return;
        }

        for (int i = 0; i < nums.length; i++) {
            if (visiting[i]) continue;
            visiting[i] = true;
            note.add(nums[i]);
            backtrack(nums, remain - 1, res, note, visiting);
            note.remove(note.size() - 1);
            visiting[i] = false;
        }

    }
}
```


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