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 print all possible ordering of tasks meeting all prerequisites.

Examples

Example 1:

Input: Tasks=4, Prerequisites=[3, 2], [3, 0], [2, 0], [2, 1]
Output: 
1) [3, 2, 0, 1]
2) [3, 2, 1, 0]
Explanation: There are two possible orderings of the tasks meeting all prerequisites.

Example 2:

Input: Tasks=3, Prerequisites=[0, 1], [1, 2]
Output: [0, 1, 2]
Explanation: There is only possible ordering of the tasks.

Example 3:

Input: Tasks=6, Prerequisites=[2, 5], [0, 5], [0, 4], [1, 4], [3, 2], [1, 3]
Output: 
1) [0, 1, 4, 3, 2, 5]
2) [0, 1, 3, 4, 2, 5]
3) [0, 1, 3, 2, 4, 5]
4) [0, 1, 3, 2, 5, 4]
5) [1, 0, 3, 4, 2, 5]
6) [1, 0, 3, 2, 4, 5]
7) [1, 0, 3, 2, 5, 4]
8) [1, 0, 4, 3, 2, 5]
9) [1, 3, 0, 2, 4, 5]
10) [1, 3, 0, 2, 5, 4]
11) [1, 3, 0, 4, 2, 5]
12) [1, 3, 2, 0, 5, 4]
13) [1, 3, 2, 0, 4, 5]