Topological Sort of Task Dependencies

Topological Sort of Task Dependencies You are given n tasks numbered from 0 to n - 1 and m directed dependency relations. Each relation a b means that task a must be completed before task b can start, i.e. there is a directed edge a -> b. Output any task execution order that satisfies every dependency. If the dependency graph contains a cycle and no valid execution order exists, output IMPOSSIBLE. Input Format n m a1 b1 a2 b2 ... am bm Output Format If a valid order exists, output n space-separated task IDs. If a cycle exists, output IMPOSSIBLE. Constraints 1 <= n <= 200,000 0 <= m <= 500,000 0 <= ai, bi < n Duplicate edges may appear. Example 1 Input: 4 3 0 1 0 2 1 3 Output: 0 1 2 3 0 2 1 3 is also valid. Example 2 Input: 3 3 0 1 1 2 2 0 Output: IMPOSSIBLE Example Input 4 3 0 1 0 2 1 3 Output 0 1 2 3