Course Schedule Variant (Topological Sort)

Given n courses labeled 0..n-1 and prerequisite pairs prerequisites, where each pair [a, b] means you must take course b before course a. Determine whether it is possible to finish all courses. If possible, output any valid course order; otherwise output IMPOSSIBLE. Input First line: two integers n and m. Next m lines: two integers a b representing edge b -> a. Output If no valid ordering exists, print IMPOSSIBLE. Otherwise print one line with n integers representing a valid ordering. Constraints 1 <= n <= 2e5 0 <= m <= 2e5 0 <= a, b < n Duplicate edges may exist. Examples See test cases in the Chinese version. Example Input 2 1 1 0 Output 0 1