Road network

from queue import Queue
from itertools import islice
import sys

n, m = [int(x) for x in input().split()]

routes = []
for i in range(0, n + 1):
    routes.append([])

for i in range(m):
    a, b = [int(x) for x in input().split()]
    routes[a].append(b)

solution = [0] * (n + 1)

# if we've reached this intersection from the currently
# processed node. The node that we care about is written into
# the array - if we havent reached it then it will be out of date -
# we can use this later on when finding an example of something that
# does not work
reached = [0] * (n + 1)

# Dynamic programming + search. Basically we go through
# each node and if we see a node for which we know that
# we can reach every other road
for i in range(1, n + 1):
    q = Queue()

    q.put(i)
    visited = [i]

    while not q.empty():
        node = q.get()
        reached[node] = i
        #visited.append(node)

        # We can reach every other node from
        # this node - mark this one in the solution
        # as well and continue
        if solution[node] == 1:
            solution[i] = 1
            break

        # Not sure yet, lets push this node's children
        # on to the queue and continue
        for c in routes[node]:
            if reached[c] != i:
                q.put(c)

    if solution[i] == 1:
        # in this case, every other node that we came from
        # can also reach this one
        # for x in visited:
        #     solution[x] = 1
        continue

    # Reached the end of the queue. Did we reach
    # every node from this one?
    for r in range(1, n + 1):
        if reached[r] != i:
            print("NO")
            print(i, r)
            sys.exit(0)
    
    solution[i] = 1

print("YES")

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: TIME LIMIT EXCEEDED

Test 7

Verdict: TIME LIMIT EXCEEDED

Test 8

Verdict: TIME LIMIT EXCEEDED

Test 9

Verdict: TIME LIMIT EXCEEDED

Test 10

Verdict: TIME LIMIT EXCEEDED

Test 11

Verdict: ACCEPTED