Problem Statement

There are ‘N’ tasks, labeled from ‘0’ to ‘N-1’. Each task can have some prerequisite tasks which need to be completed before it can be scheduled.

Given the number of tasks and a list of prerequisite pairs, write a method to find the ordering of tasks we should pick to finish all tasks.

Examples

Example 1:

Input: Tasks=6, Prerequisites=[2, 5], [0, 5], [0, 4], [1, 4], [3, 2], [1, 3]
Output: [0 1 4 3 2 5] 
Explanation: A possible scheduling of tasks is: [0 1 4 3 2 5] 

Example 2:

Input: Tasks=3, Prerequisites=[0, 1], [1, 2]
Output: [0, 1, 2]
Explanation: To execute task '1', task '0' needs to finish first. Similarly, task '1' needs to finish before '2' can be scheduled. A possible scheduling of tasks is: [0, 1, 2] 

Example 3:

Input: Tasks=3, Prerequisites=[0, 1], [1, 2], [2, 0]
Output: []
Explanation: The tasks have a cyclic dependency, therefore they cannot be scheduled.