Buggy python submission (verdict: Runtime Error):
from collections import defaultdict
from functools import lru_cache
import sys
sys.setrecursionlimit(1000000)


N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)


@lru_cache(N)
def depth(n):
    ret = -1
    for y in x_to_y[n]:
        ret = max(ret, depth(y))
    return ret + 1


        
depths = [depth(n) for n in range(1, N + 1)]
print(max(depths), default=0)


Fixed submission:
from collections import defaultdict
from functools import lru_cache
import sys
sys.setrecursionlimit(1000000)


N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)


@lru_cache(N)
def depth(n):
    ret = -1
    for y in x_to_y[n]:
        ret = max(ret, depth(y))
    return ret + 1


        
depths = [depth(n) for n in range(1, N + 1)]
print(max(depths))

Buggy python submission (verdict: Runtime Error):
from collections import defaultdict
from functools import lru_cache

N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)


@lru_cache(N)
def depth(n):
    ret = -1
    for y in x_to_y[n]:
        ret = max(ret, depth(y))
    return ret + 1


        
depths = [depth(n) for n in range(1, N + 1)]
print(max(depths), default=0)


Fixed submission:
from collections import defaultdict
from functools import lru_cache
import sys
sys.setrecursionlimit(1000000)


N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)


@lru_cache(N)
def depth(n):
    ret = -1
    for y in x_to_y[n]:
        ret = max(ret, depth(y))
    return ret + 1


        
depths = [depth(n) for n in range(1, N + 1)]
print(max(depths))

Buggy python submission (verdict: Runtime Error):
from collections import defaultdict
from functools import lru_cache

N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)


@lru_cache(N)
def depth(n):
    ret = -1
    for y in x_to_y[n]:
        ret = max(ret, depth(y))
    return ret + 1


        
depths = [depth(n) for n in range(1, N + 1)]
print(max(depths))


Fixed submission:
from collections import defaultdict
from functools import lru_cache
import sys
sys.setrecursionlimit(1000000)


N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)


@lru_cache(N)
def depth(n):
    ret = -1
    for y in x_to_y[n]:
        ret = max(ret, depth(y))
    return ret + 1


        
depths = [depth(n) for n in range(1, N + 1)]
print(max(depths))

Buggy python submission (verdict: Runtime Error):
from collections import defaultdict
from functools import lru_cache

N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)


@lru_cache(N)
def depth(n):
    ret = -1
    for y in x_to_y[n]:
        ret = max(ret, depth(y))
    return ret + 1


        
depths = [depth(n) for n in range(1, N + 1)]
print(max(depths))


Fixed submission:
from collections import defaultdict
from functools import lru_cache
import sys
sys.setrecursionlimit(1000000)


N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)


@lru_cache(N)
def depth(n):
    ret = -1
    for y in x_to_y[n]:
        ret = max(ret, depth(y))
    return ret + 1


        
depths = [depth(n) for n in range(1, N + 1)]
print(max(depths))

Buggy python submission (verdict: Time Limit Exceeded):
from collections import defaultdict

N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
y_to_x = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)
    y_to_x[y].append(x)

# 終端をサーチ
ends = [x for x in range(1, N  +1) if x not in x_to_y.keys()]
starts = [y for y in range(1, N + 1) if y not in y_to_x.keys()]

def search_next(current):
    # まだ探索していない前のノードがあればそちらを優先する
    for y in x_to_y[current]:
        if dp[y] == -1:
            continue

    for next_node in y_to_x[current]:
        dp[next_node] = max(dp[next_node], dp[current] + 1)
        search_next(next_node)


        

for end in ends:
    dp[end] = 0
    search_next(end)

print(max(dp))


Fixed submission:
from collections import defaultdict
from functools import lru_cache
import sys
sys.setrecursionlimit(1000000)


N, M = map(int, input().split())
XY = [map(int, input().split()) for _ in range(M)]

dp = [-1 for _ in range(N + 1)]

x_to_y = defaultdict(list)
for x, y in XY:
    x_to_y[x].append(y)


@lru_cache(N)
def depth(n):
    ret = -1
    for y in x_to_y[n]:
        ret = max(ret, depth(y))
    return ret + 1


        
depths = [depth(n) for n in range(1, N + 1)]
print(max(depths))