AP2 2018-05-10

P56483.py

from jutge import read


def dfs(G, u, y, vis):
    if not vis[u]:
        vis[u] = True
        for v in G[u]:
            if vis[y]:
                return
            dfs(G, v, y, vis)


def main():
    n, m = read(int, int)
    G = [[] for i in range(n)]
    for i in range(m):
        u, v = read(int, int)
        G[u].append(v)
    x, y = read(int, int)

    vis = [False for i in range(n)]
    dfs(G, x, y, vis)

    print("yes" if vis[y] else "no")


main()