### Problem

Given an array `a`

, find all its subsets

For example, array `[1, 2, 3]`

will have the following subsets

```
[]
[1]
[1, 2]
[1, 2, 3]
[1, 3]
[2]
[2, 3]
[3]
```

### Backtracking approach

```
```

Given an array `a`

, find all its subsets

For example, array `[1, 2, 3]`

will have the following subsets

```
[]
[1]
[1, 2]
[1, 2, 3]
[1, 3]
[2]
[2, 3]
[3]
```

```
```