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Problem of the day

You are given an array/list 'ARR' consisting of N integers, which contains elements only in the range 0 to N - 1. Some of the elements may be repeated in 'ARR'. Your task is to find all such duplicate elements.

```
1. All the elements are in the range 0 to N - 1.
2. The elements may not be in sorted order.
3. You can return the duplicate elements in any order.
4. If there are no duplicates present then return an empty array.
```

Detailed explanation

```
1 <= T <= 10^2
1 <= N <= 10^4
0 <= ARR[i] <= N - 1
Time Limit: 1 sec
```

```
2
5
0 2 1 2 3
7
3 2 1 3 2 1 5
```

```
2
1 2 3
```

```
For the first test case, since 2 is the only duplicate element, so we return it.
For the second test case, since 1, 2, 3 are duplicates so we return them. Note that 2, 3, 1 and 3, 2, 1 are also acceptable.
```

```
1
3
0 1 2
```

```
-1
```

```
For the first test case, since there are no duplicates we return -1.
```