Permutations

Combination Sum

Find Median from Data Stream

Generate every ordering of a distinct integer array.

Return every permutation of distinct `nums` in depth-first input-choice order.

## Example
```json
Input: {"nums":[1,2,3]}
Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
```

## Constraints
- 1 <= nums.length <= 7
- All values are unique

## Follow-up
How can in-place swapping reduce per-branch allocations?

The key pattern is: Backtracking chooses each remaining value next. Identify the state and invariant before coding.

Recognize the Pattern

Advance one state transition at a time. Mark or update state before exploring dependent work.

Build the Algorithm

Test empty or minimal input, skewed shapes, duplicates where allowed, and impossible outcomes.