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):
#!/usr/bin/env python3
from collections import defaultdict,deque
from heapq import heappush, heappop
from bisect import bisect_left, bisect_right
import sys, random, itertools, math
sys.setrecursionlimit(10**5)
input = sys.stdin.readline
sqrt = math.sqrt
def LI(): return list(map(int, input().split()))
def LF(): return list(map(float, input().split()))
def LI_(): return list(map(lambda x: int(x)-1, input().split()))
def II(): return int(input())
def IF(): return float(input())
def LS(): return list(map(list, input().split()))
def S(): return list(input().rstrip())
def IR(n): return [II() for _ in range(n)]
def LIR(n): return [LI() for _ in range(n)]
def FR(n): return [IF() for _ in range(n)]
def LFR(n): return [LI() for _ in range(n)]
def LIR_(n): return [LI_() for _ in range(n)]
def SR(n): return [S() for _ in range(n)]
def LSR(n): return [LS() for _ in range(n)]
mod = 1000000007
inf = float('INF')
import time

#A
def A():
    s = S()
    t = S()
    ans = 0
    for i in range(3):
        if s[i] == t[i]:
            ans += 1
    print(ans)
    return

#B
def B():
    a, b = LI()
    ans = 0
    b -= 1
    while b > 0:
        b -= a - 1
        ans += 1
    print(ans)

    return

#C
def C():
    n = II()
    h = LI()
    i = 0
    ans = 0
    while i < n:
        down = i+1
        while down < n:
            if h[down - 1] >= h[down]:
                down += 1
            else:
                break
        ans = max(ans, down - i - 1)
        i = down
    print(ans)
    return

#D
def D():
    n = II()
    print(n * (n - 1) // 2)
    return

#E
def E():
    start = time.time()
    n = II()
    a = LIR_(n)
    ans = 0
    tern = [0] * n
    while 1:
        ans += 1
        f = True
        c = defaultdict(int)
        for i in range(n):
            if c[i]:
                continue
            if tern[i] == n - 1:
                continue
            rival = a[i][tern[i]]
            if c[rival]:
                continue
            if tern[rival] == n - 1:
                continue
            if a[rival][tern[rival]] == i:
                c[i] += 1
                c[rival] += 1
                tern[rival] += 1
                tern[i] += 1
                f = False
        if time.time - start >= 1.8:
            print(n * (n - 1) // 2)
            return
        if f:
            if tern == [n - 1] * n:
                print(ans-1)
                return
            else:
                print(-1)
                return
    return

#F
def F():
    return

#Solve
if __name__ == '__main__':
    E()


#!/usr/bin/env python3
from collections import defaultdict,deque
from heapq import heappush, heappop
from bisect import bisect_left, bisect_right
import sys, random, itertools, math
sys.setrecursionlimit(10**5)
input = sys.stdin.readline
sqrt = math.sqrt
def LI(): return list(map(int, input().split()))
def LF(): return list(map(float, input().split()))
def LI_(): return list(map(lambda x: int(x)-1, input().split()))
def II(): return int(input())
def IF(): return float(input())
def LS(): return list(map(list, input().split()))
def S(): return list(input().rstrip())
def IR(n): return [II() for _ in range(n)]
def LIR(n): return [LI() for _ in range(n)]
def FR(n): return [IF() for _ in range(n)]
def LFR(n): return [LI() for _ in range(n)]
def LIR_(n): return [LI_() for _ in range(n)]
def SR(n): return [S() for _ in range(n)]
def LSR(n): return [LS() for _ in range(n)]
mod = 1000000007
inf = float('INF')
import time

#A
def A():
    s = S()
    t = S()
    ans = 0
    for i in range(3):
        if s[i] == t[i]:
            ans += 1
    print(ans)
    return

#B
def B():
    a, b = LI()
    ans = 0
    b -= 1
    while b > 0:
        b -= a - 1
        ans += 1
    print(ans)

    return

#C
def C():
    n = II()
    h = LI()
    i = 0
    ans = 0
    while i < n:
        down = i+1
        while down < n:
            if h[down - 1] >= h[down]:
                down += 1
            else:
                break
        ans = max(ans, down - i - 1)
        i = down
    print(ans)
    return

#D
def D():
    n = II()
    print(n * (n - 1) // 2)
    return

#E
def E():
    start = time.time()
    n = II()
    a = LIR_(n)
    ans = 0
    tern = [0] * n
    while 1:
        ans += 1
        f = True
        c = defaultdict(int)
        for i in range(n):
            if c[i]:
                continue
            if tern[i] == n - 1:
                continue
            rival = a[i][tern[i]]
            if c[rival]:
                continue
            if tern[rival] == n - 1:
                continue
            if a[rival][tern[rival]] == i:
                c[i] += 1
                c[rival] += 1
                tern[rival] += 1
                tern[i] += 1
                f = False
        if time.time() - start >= 1:
            print(n * (n - 1) // 2)
            return
        if f:
            if tern == [n - 1] * n:
                print(ans-1)
                return
            else:
                print(-1)
                return
    return

#F
def F():
    return

#Solve
if __name__ == '__main__':
    E()


Verdicts: Runtime Error

Accepted