Problem: N players will participate in a tennis tournament. We will call them Player 1, Player 2, \ldots, Player N.  The tournament is round-robin format, and there will be N(N-1)/2 matches in total. Is it possible to schedule these matches so that all of the following conditions are satisfied? If the answer is yes, also find the minimum number of days required.    * Each player plays at most one matches in a day.   * Each player i (1 \leq i \leq N) plays one match against Player A_{i, 1}, A_{i, 2}, \ldots, A_{i, N-1} in this order.

Submission attempts (in order):
import sys
sys.setrecursionlimit(1000000)
N = int(input())

match = [[-1] * (N) for _ in range(N)]
c = 0
for i in range(N):
    for j in range(i+1, N):
        match[i][j] = c
        c += 1


def get_id(i, j):
    if i > j:
        i, j = j, i
    return match[i][j]


start = []
G = {k: [] for k in range(c)}
for i in range(N):
    L = map(int, input().split())
    pid = -1
    for j, l in enumerate(L):
        id = get_id(i, l-1)
        if j == 0:
            start.append(id)
        else:
            G[pid].append(id)
        pid = id

visited = [False]*c
dp = [-1]*c


def dfs(v):
    if dp[v] >= 0:
        return dp[v]
    visited[v] = True
    dp[v] = 1
    for nxt in G[v]:
        if visited[nxt] is True:
            print(-1)
            exit()
        d = dfs(nxt)
        if d >= dp[v]:
            dp[v] = d+1
    return dp[v]


ans = 0
for i in start:
    res = dfs(i)
    ans = max(ans, res)
print(ans)


import sys
sys.setrecursionlimit(1000000)
N = int(input())

match = [[-1] * (N) for _ in range(N)]
c = 0
for i in range(N):
    for j in range(i+1, N):
        match[i][j] = c
        c += 1
# print(match)


def get_id(i, j):
    if i > j:
        i, j = j, i
    return match[i][j]


G = {k: [] for k in range(c)}
for i in range(N):
    L = map(int, input().split())
    pid = -1
    for l in L:
        id = get_id(i, l-1)
        if pid != -1:
            G[id].append(pid)
        pid = id

visited = [False]*c
calculated = [False]*c
dp = [-1]*c


def dfs(v):
    if dp[v] >= 0:
        return dp[v]
    visited[v] = True
    dp[v] = 1
    for nxt in G[v]:
        if visited[nxt] is True and calculated[nxt] is False:
            print(-1)
            exit()
        if visited[nxt] is False:
            dp[v] = max(dp[v], dfs(nxt)+1)
    calculated[v] = True
    return dp[v]


ans = 0
for i in range(c):
    res = dfs(i)
    ans = max(ans, res)
print(ans)


import sys
sys.setrecursionlimit(1000000)
N = int(input())

match = [[-1] * (N) for _ in range(N)]
c = 0
for i in range(N):
    for j in range(i+1, N):
        match[i][j] = c
        c += 1


def get_id(i, j):
    if i > j:
        i, j = j, i
    return match[i][j]


start = []
G = {k: [] for k in range(c)}
for i in range(N):
    L = map(int, input().split())
    pid = -1
    for i, l in enumerate(L):
        id = get_id(i, l-1)
        if i == 0:
            start.append(id)
        else:
            G[pid].append(id)
        pid = id

visited = [False]*c
calculated = [False]*c
dp = [-1]*c


def dfs(v):
    if dp[v] >= 0:
        return dp[v]
    visited[v] = True
    dp[v] = 1
    for nxt in G[v]:
        if visited[nxt] is True and calculated[nxt] is False:
            print(-1)
            exit()
        d = dfs(nxt)
        if d >= dp[v]:
            dp[v] = d+1
    calculated[v] = True
    return dp[v]


ans = 0
for i in start:
    res = dfs(i)
    ans = max(ans, res)
print(ans)


import sys
sys.setrecursionlimit(1000000)
N = int(input())

match = [[-1] * (N) for _ in range(N)]
c = 0
for i in range(N):
    for j in range(i+1, N):
        match[i][j] = c
        c += 1


def get_id(i, j):
    if i > j:
        i, j = j, i
    return match[i][j]


start = []
G = {k: [] for k in range(c)}
for i in range(N):
    L = map(int, input().split())
    pid = -1
    for i, l in enumerate(L):
        id = get_id(i, l-1)
        if i == 0:
            start.append(id)
        else:
            G[pid].append(id)
        pid = id

visited = [False]*c
calculated = [False]*c
dp = [-1]*c


def dfs(v):
    if dp[v] >= 0:
        return dp[v]
    visited[v] = True
    dp[v] = 1
    for nxt in G[v]:
        if visited[nxt] is True and calculated[nxt] is False:
            print(-1)
            exit()
        d = dfs(nxt)
        if d >= dp[v]:
            dp[v] = d+1
    calculated[v] = True
    return dp[v]


ans = 0
for i in start:
    res = dfs(i)
    ans = max(ans, res)
print(ans)


from collections import deque

N = int(input())
L = [deque([int(i)-1 for i in input().split()]) for i in range(N)]

q = deque(range(N))
d = [0 for i in range(N)]
pairs = [-1 for i in range(N)]
while q:
    a = q.popleft()  
    if len(L[a]) == 0:
        continue
    b = L[a].popleft()

    if pairs[b] == a:  
        d[a] = d[b] = max(d[a], d[b]) + 1
        q.append(a)
        q.append(b)
    else:
        pairs[a] = b
print(max(d) if not any(L) else -1)


Verdicts: Wrong Answer

Wrong Answer

Runtime Error

Runtime Error

Accepted