# Topological Sorting

## Problem

Given an directed graph, a topological order of the graph nodes is defined as follow:

- For each directed edge
`A -> B`

in graph,`A`

must before`B`

in the order list. - The first node in the order can be any node in the graph with no nodes direct to it.

Find any topological order for the given graph.

Notice: You can assume that there is at least one topological order in the graph.

### Example

For graph as follow:

The topological order can be:

```
[0, 1, 2, 3, 4, 5]
[0, 2, 3, 1, 5, 4]
...
```