Topological orderings

There are $n$ tasks, which have to be done one by one. Some tasks must be done before others: there are $m$ precedence relations between tasks. Write a program that prints all possible ways to order the $n$ tasks according to the $m$ given precedences.

Input

Input consists of a natural number $n \ge 1$ , followed by a natural number $m$ , followed by $m$ different pairs $x, y$ , indicating that task $x$ must be done before task $y$ . Suppose that the tasks are numbered from 0 to $n - 1$ .

Output

Print, one per line and in lexicographic order, all the ways of sorting the $n$ tasks according to the $m$ given precedences. There will always be at least one solution.

Problem information

Author: Unknown
Translator: Salvador Roura

Generation: 2026-01-25T11:12:09.662Z