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Given two integers n and k. Return all possible combinations of k numbers out of 1, 2, ... , n.

```
Input: n = 4, k = 2
Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
```

```
Input: n = 4, k = 1
Output: [[1],[2 …
```

Give a string, you can choose to split the string after one character or two adjacent characters, and make the string to be composed of only one character or two characters. Output all possible results.

```
Input: "123"
Output: [["1","2","3"],["12","3"],["1","23"]]
```

`Input …`