A tournament is a directed graph with exactly one edge between every pair of vertices. (So for each pair (u,v) of vertices, either the edge from u to v or from v to u exists, but not both.) You can think of the nodes as players in a tournament, where each player has to play against every other player. The edge points from the winner to the loser of a game. A Hamiltonian path (not cycle) is a sequence of consecutive directed edges that visits every vertex exactly once.
How can i prove that every tournament contains at least one Hamiltonian path? thanks your help!