Determine Players with Fixed Rankings

Problem: Determine Players with Fixed Rankings There are N players, numbered from 1 to N, and M match results. Each result (winner, loser) means that winner defeated loser. The win relation is transitive: if A defeated B and B defeated C, then A can be inferred to have defeated C. A player's final rank is considered determinable if the available results and their transitive implications determine that player's win/loss relation with every other player. In other words, for every other player q, either p can be inferred to defeat q, or q can be inferred to defeat p. Output all players whose ranks are determinable, in ascending order, and the number of such players. The input is guaranteed to contain no contradictions: there are no distinct players a and b such that both a defeats b and b defeats a can be inferred. Input Format First line: two integers N M Next M lines: two integers winner loser Output Format First line: the number K of players with determinable ranks Second line: K player IDs in ascending order. If K = 0, output an empty line. Constraints 1 <= N <= 500 0 <= M <= N * (N - 1) / 2 Example Input 5 5 1 2 2 3 3 4 4 5 1 3 Output 5 1 2 3 4 5 Example Input 5 5 1 2 2 3 3 4 4 5 1 3 Output 5 1 2 3 4 5