## 46. Permutations

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.

## Rust Solution

``````struct Solution;

impl Solution {
fn permute_r(arr: &mut Vec<i32>, start: usize, length: usize, res: &mut Vec<Vec<i32>>) {
if start == length {
res.push(arr.to_vec());
return;
}
for i in start..length {
arr.swap(start, i);
Self::permute_r(arr, start + 1, length, res);
arr.swap(start, i);
}
}

fn permute(mut nums: Vec<i32>) -> Vec<Vec<i32>> {
let mut res = vec![];
let n = nums.len();
Self::permute_r(&mut nums, 0, n, &mut res);
res
}
}

#[test]
fn test() {
let nums = vec![1, 2, 3];
let mut ans: Vec<Vec<i32>> = [
[1, 2, 3],
[1, 3, 2],
[2, 1, 3],
[2, 3, 1],
[3, 1, 2],
[3, 2, 1],
]
.iter()
.map(|v| v.to_vec())
.collect();
let mut res = Solution::permute(nums);
ans.sort_unstable();
res.sort_unstable();
assert_eq!(res, ans);
}
``````

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