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You are given an unsorted array/list 'ARR' of 'N' integers. Your task is to return the length of the longest consecutive sequence.

The consecutive sequence is in the form ['NUM', 'NUM' + 1, 'NUM' + 2, ..., 'NUM' + L] where 'NUM' is the starting integer of the sequence and 'L' + 1 is the length of the sequence.

Note:

```
If there are any duplicates in the given array we will count only one of them in the consecutive sequence.
```

```
For the given 'ARR' [9,5,4,9,10,10,6].
Output = 3
The longest consecutive sequence is [4,5,6].
```

```
Can you solve this in O(N) time and O(N) space complexity?
```

Detailed explanation

```
1 <= T <= 10
1 <= N <= 10^5
-10^9 <= ARR[i] <= 10^9
Time Limit: 1 sec
```

```
1
5
33 20 34 30 35
```

```
3
```

```
The longest consecutive sequence is [33, 34, 35].
```

```
1
7
1 9 3 10 4 20 2
```

```
4
```

```
The consecutive sequence is in the form ['NUM', 'NUM' + 1, 'NUM' + 2,...,'NUM' + 'L']. So in the given array, the longest consecutive sequence is [1,2,3,4] where 'NUM' = 1 and 'L' = 3. And the length of the sequence will be 'L' + 1 = 4.
```