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You are given a * ‘Binary Tree’*.

Return the preorder traversal of the Binary Tree.

```
Input: Consider the following Binary Tree:
```

```
Output:
Following is the preorder traversal of the given Binary Tree: [1, 2, 5, 3, 6, 4]
```

Detailed explanation

```
1 2 3 5 4 6 7 -1 -1 -1 -1 -1 -1 -1 -1
```

```
1 2 5 4 3 6 7
```

```
The Binary Tree given in the input is as follows:
```

```
5 6 10 2 3 -1 -1 -1 -1 -1 9 -1 -1
```

```
5 6 2 3 9 10
```

```
The Binary Tree given in the input is as follows:
```

```
Try to do this in O(n).
```

```
1 <= n <= 100000
where 'n' is the number of nodes in the binary tree.
Time Limit: 1 sec
```