# 46. Permutations (Medium)

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

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]
]
```

## Solutions

``````class Solution {
public List<List<Integer>> permute(int[] nums) {
List<List<Integer>> ans = new ArrayList<>();
if (nums == null || nums.length == 0) {
return ans;
}

doPermutation(nums, ans, 0);

return ans;
}

private void doPermutation(int[] nums, List<List<Integer>> ans, int depth) {
int len = nums.length;

if (depth == len - 1) {
List<Integer> solution = new ArrayList<>();
for (int n : nums) {
}

return;
}

// For depth = 0, this first slot could be len situations from num[0] to num[len-1]
// Once the first slot determined, continue to go through rest elemennts
for (int j = depth; j < len; j++) {
swap(nums, depth, j);

doPermutation(nums, ans, depth + 1);

swap(nums, depth, j);
}
}

void swap(int[] nums, int x, int y) {
int tmp = nums[x];
nums[x] = nums[y];
nums[y] = tmp;
}
}
``````