Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input = sys.stdin.readline
    from collections import deque
    from collections import defaultdict

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # O(N)
    def is_not_empty():
        for x in A:
            if x:
                return True
        return False

    answer = 0
    while is_not_empty():
        played = defaultdict(int)
        for i in range(1,N+1):
            if played[i] == 1:
                continue
            if not A[i]:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and played[enemy] == 0:
                played[enemy] = 1
                played[ME] = 1
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not played:
            print(-1)
            exit()
        answer += 1

    print(answer)

if __name__ == '__main__':
    main()

Fixed submission:
# O(N)
def is_not_empty(A):
    for x in A:
        if x:
            return True
    return False

def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # 当日の参加者
    today = set()
    # 初日
    for i in range(1,N+1):
        # 既に参加した人はダメ
        if i in today:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in today):
            today.add(ME)
            today.add(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    # 初日に誰も試合できなかったとき
    if not today:
        print(-1)
        exit()

    # 前日の参加者
    yesterday = today
    # 日数
    answer = 1
    while is_not_empty(A):
        today = set()
        # 前日に試合した人は必ず次の日に試合する
        for i in yesterday:
            if not A[i]:
                continue
            if i in today:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in today):
                today.add(ME)
                today.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not today:
            print(-1)
            exit()
        answer += 1
        yesterday = today

    print(answer)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input = sys.stdin.readline
    from collections import deque
    from collections import defaultdict

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # O(N)
    def is_not_empty():
        for x in A:
            if x:
                return True
        return False

    answer = 0
    while is_not_empty():
        played = defaultdict(int)
        for i in range(1,N+1):
            if played[i] == 1:
                continue
            if not A[i]:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and played[enemy] == 0:
                played[enemy] = 1
                played[ME] = 1
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not played:
            print(-1)
            exit()
        answer += 1

    print(answer)

if __name__ == '__main__':
    main()

Fixed submission:
# O(N)
def is_not_empty(A):
    for x in A:
        if x:
            return True
    return False

def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # 当日の参加者
    today = set()
    # 初日
    for i in range(1,N+1):
        # 既に参加した人はダメ
        if i in today:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in today):
            today.add(ME)
            today.add(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    # 初日に誰も試合できなかったとき
    if not today:
        print(-1)
        exit()

    # 前日の参加者
    yesterday = today
    # 日数
    answer = 1
    while is_not_empty(A):
        today = set()
        # 前日に試合した人は必ず次の日に試合する
        for i in yesterday:
            if not A[i]:
                continue
            if i in today:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in today):
                today.add(ME)
                today.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not today:
            print(-1)
            exit()
        answer += 1
        yesterday = today

    print(answer)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input = sys.stdin.readline
    from collections import deque
    from collections import defaultdict

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # O(N)
    def is_not_empty():
        for x in A:
            if x:
                return True
        return False

    answer = 0
    while is_not_empty():
        played = defaultdict(int)
        for i in range(1,N+1):
            if i in played:
                continue
            if not A[i]:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and played[enemy] == 0:
                played[enemy] += 1
                played[ME] += 1
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not played:
            print(-1)
            exit()
        answer += 1

    print(answer)

if __name__ == '__main__':
    main()

Fixed submission:
# O(N)
def is_not_empty(A):
    for x in A:
        if x:
            return True
    return False

def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # 当日の参加者
    today = set()
    # 初日
    for i in range(1,N+1):
        # 既に参加した人はダメ
        if i in today:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in today):
            today.add(ME)
            today.add(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    # 初日に誰も試合できなかったとき
    if not today:
        print(-1)
        exit()

    # 前日の参加者
    yesterday = today
    # 日数
    answer = 1
    while is_not_empty(A):
        today = set()
        # 前日に試合した人は必ず次の日に試合する
        for i in yesterday:
            if not A[i]:
                continue
            if i in today:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in today):
                today.add(ME)
                today.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not today:
            print(-1)
            exit()
        answer += 1
        yesterday = today

    print(answer)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # O(N)
    def is_not_empty():
        for x in A:
            if x:
                return True
        return False

    answer = 0
    while is_not_empty():
        if answer == N*(N-1)//2:
            print(-1)
            exit()
        played = set()
        for i in range(1,N+1):
            if i in played:
                continue
            if not A[i]:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in played):
                played.add(ME)
                played.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not played:
            print(-1)
            exit()
        answer += 1

    print(answer)

if __name__ == '__main__':
    main()

Fixed submission:
# O(N)
def is_not_empty(A):
    for x in A:
        if x:
            return True
    return False

def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # 当日の参加者
    today = set()
    # 初日
    for i in range(1,N+1):
        # 既に参加した人はダメ
        if i in today:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in today):
            today.add(ME)
            today.add(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    # 初日に誰も試合できなかったとき
    if not today:
        print(-1)
        exit()

    # 前日の参加者
    yesterday = today
    # 日数
    answer = 1
    while is_not_empty(A):
        today = set()
        # 前日に試合した人は必ず次の日に試合する
        for i in yesterday:
            if not A[i]:
                continue
            if i in today:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in today):
                today.add(ME)
                today.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not today:
            print(-1)
            exit()
        answer += 1
        yesterday = today

    print(answer)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # O(N)
    def is_not_empty():
        for x in A:
            if x:
                return True
        return False

    answer = 0
    while is_not_empty():
        played = set()
        for i in range(1,N+1):
            if i in played:
                continue
            if not A[i]:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in played):
                played.add(ME)
                played.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not played:
            print(-1)
            exit()
        answer += 1

    print(answer)

if __name__ == '__main__':
    main()

Fixed submission:
# O(N)
def is_not_empty(A):
    for x in A:
        if x:
            return True
    return False

def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # 当日の参加者
    today = set()
    # 初日
    for i in range(1,N+1):
        # 既に参加した人はダメ
        if i in today:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in today):
            today.add(ME)
            today.add(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    # 初日に誰も試合できなかったとき
    if not today:
        print(-1)
        exit()

    # 前日の参加者
    yesterday = today
    # 日数
    answer = 1
    while is_not_empty(A):
        today = set()
        # 前日に試合した人は必ず次の日に試合する
        for i in yesterday:
            if not A[i]:
                continue
            if i in today:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in today):
                today.add(ME)
                today.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not today:
            print(-1)
            exit()
        answer += 1
        yesterday = today

    print(answer)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # O(N)
    def is_not_empty():
        for x in A:
            if x:
                return True
        return False

    answer = 0
    while is_not_empty():
        played = set()
        for i in range(1,N+1):
            if i in played:
                continue
            if not A[i]:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in played):
                played.add(ME)
                played.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if len(played) == 0:
            print(-1)
            exit()
        answer += 1

    print(answer)

if __name__ == '__main__':
    main()

Fixed submission:
# O(N)
def is_not_empty(A):
    for x in A:
        if x:
            return True
    return False

def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # 当日の参加者
    today = set()
    # 初日
    for i in range(1,N+1):
        # 既に参加した人はダメ
        if i in today:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in today):
            today.add(ME)
            today.add(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    # 初日に誰も試合できなかったとき
    if not today:
        print(-1)
        exit()

    # 前日の参加者
    yesterday = today
    # 日数
    answer = 1
    while is_not_empty(A):
        today = set()
        # 前日に試合した人は必ず次の日に試合する
        for i in yesterday:
            if not A[i]:
                continue
            if i in today:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in today):
                today.add(ME)
                today.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not today:
            print(-1)
            exit()
        answer += 1
        yesterday = today

    print(answer)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # i-indexed
    A = [deque() for _ in range(N+1)]
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    def is_not_empty():
        for x in A:
            if len(x) != 0:
                return True
        return False

    answer = 0
    while is_not_empty():
        played = set()
        for i in range(1,N+1):
            if i in played:
                continue
            if len(A[i]) == 0:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in played):
                played.add(ME)
                played.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if len(played) == 0:
            print(-1)
            exit()
        answer += 1

    print(answer)

if __name__ == '__main__':
    main()

Fixed submission:
# O(N)
def is_not_empty(A):
    for x in A:
        if x:
            return True
    return False

def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # 当日の参加者
    today = set()
    # 初日
    for i in range(1,N+1):
        # 既に参加した人はダメ
        if i in today:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in today):
            today.add(ME)
            today.add(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    # 初日に誰も試合できなかったとき
    if not today:
        print(-1)
        exit()

    # 前日の参加者
    yesterday = today
    # 日数
    answer = 1
    while is_not_empty(A):
        today = set()
        # 前日に試合した人は必ず次の日に試合する
        for i in yesterday:
            if not A[i]:
                continue
            if i in today:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in today):
                today.add(ME)
                today.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not today:
            print(-1)
            exit()
        answer += 1
        yesterday = today

    print(answer)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline
from collections import deque
sys.setrecursionlimit(10 ** 7)

N = int(input())
# i-indexed
A = [deque() for _ in range(N+1)]
for i in range(1,N+1):
    for j in input().split():
        A[i].append(int(j))

def is_not_empty():
    for x in A:
        if len(x) != 0:
            return True
    return False

answer = 0
while is_not_empty():
    played = []
    append = played.append
    for i in range(1,N+1):
        if i in played:
            continue
        if len(A[i]) == 0:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in played):
            append(ME)
            append(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    if len(played) == 0:
        print(-1)
        exit()
    answer += 1

print(answer)

Fixed submission:
# O(N)
def is_not_empty(A):
    for x in A:
        if x:
            return True
    return False

def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # 当日の参加者
    today = set()
    # 初日
    for i in range(1,N+1):
        # 既に参加した人はダメ
        if i in today:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in today):
            today.add(ME)
            today.add(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    # 初日に誰も試合できなかったとき
    if not today:
        print(-1)
        exit()

    # 前日の参加者
    yesterday = today
    # 日数
    answer = 1
    while is_not_empty(A):
        today = set()
        # 前日に試合した人は必ず次の日に試合する
        for i in yesterday:
            if not A[i]:
                continue
            if i in today:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in today):
                today.add(ME)
                today.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not today:
            print(-1)
            exit()
        answer += 1
        yesterday = today

    print(answer)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline
from collections import deque

N = int(input())
# i-indexed
A = [deque() for _ in range(N+1)]
for i in range(1,N+1):
    for j in input().split():
        A[i].append(int(j))

def is_not_empty():
    for x in A:
        if len(x) != 0:
            return True
    return False

answer = 0
while is_not_empty():
    played = []
    append = played.append
    for i in range(1,N+1):
        if i in played:
            continue
        if len(A[i]) == 0:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in played):
            append(ME)
            append(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    if len(played) == 0:
        print(-1)
        exit()
    answer += 1

print(answer)

Fixed submission:
# O(N)
def is_not_empty(A):
    for x in A:
        if x:
            return True
    return False

def main():
    import sys
    input = sys.stdin.readline
    from collections import deque

    N = int(input())
    # 1-indexed
    A = [deque() for _ in range(N+1)]
    # O(N^2)
    for i in range(1,N+1):
        for j in input().split():
            A[i].append(int(j))

    # 当日の参加者
    today = set()
    # 初日
    for i in range(1,N+1):
        # 既に参加した人はダメ
        if i in today:
            continue
        enemy = A[i].popleft()
        ME = A[enemy].popleft()
        if ME == i and not(enemy in today):
            today.add(ME)
            today.add(enemy)
        else:
            A[i].appendleft(enemy)
            A[enemy].appendleft(ME)
    # 初日に誰も試合できなかったとき
    if not today:
        print(-1)
        exit()

    # 前日の参加者
    yesterday = today
    # 日数
    answer = 1
    while is_not_empty(A):
        today = set()
        # 前日に試合した人は必ず次の日に試合する
        for i in yesterday:
            if not A[i]:
                continue
            if i in today:
                continue
            enemy = A[i].popleft()
            ME = A[enemy].popleft()
            if ME == i and not(enemy in today):
                today.add(ME)
                today.add(enemy)
            else:
                A[i].appendleft(enemy)
                A[enemy].appendleft(ME)
        if not today:
            print(-1)
            exit()
        answer += 1
        yesterday = today

    print(answer)

if __name__ == '__main__':
    main()