Buggy python submission (verdict: Time Limit Exceeded):
import sys
n = int(input())
a = list(map(int, input().split()))
ans = 0
flag = 0
if n % 2 == 1:
  if a.count(0) != 1:
    print(0)
    sys.exit()
  else:
    sa = n-1
    while sa > 0:
      if a.count(sa) != 2:
        print(0)
        sys.exit()
      sa -= 2
else:
  if a.count(0) != 0:
    print(0)
    sys.exit()
  else:
    sa = n-1
    while sa > 0:
      if a.count(sa) != 2:
        print(0)
        sys.exit()
      sa -= 2


print(2 ** (n // 2))


Fixed submission:
import math
N = int(input())


A = list(map(int, input().split()))

A.sort()
ans = 0
flag = True
if N % 2 == 1:
  # 0,2,2,4,4,～みたいに並んでるはず
  if A[0] == 0:
    for i in range(1,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)

else:
  if A[0] != 0:
    for i in range(0,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)
    
    
    
print(ans)

Buggy python submission (verdict: Runtime Error):
import sys
n = int(input())
a = list(map(int, input().split()))
ans = 0
flag = 0
if n % 2 == 1:
  if a.count(0) != 1: flag = 1
  else:
    sa = n-1
    while sa > 0:
      if a.count(sa) != 2:
        print(0)
        sys.exit()
      sa -= 2
else:
  if a.count(0) != 0: flag = 1
  else:
    sa = n-1
    while sa > 0:
      if a.count(sa) != 2:
        print(0
        sys.exit()
      sa -= 2

if flag == 0:
  print(2 ** (n // 2))
else:
  print(0)

Fixed submission:
import math
N = int(input())


A = list(map(int, input().split()))

A.sort()
ans = 0
flag = True
if N % 2 == 1:
  # 0,2,2,4,4,～みたいに並んでるはず
  if A[0] == 0:
    for i in range(1,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)

else:
  if A[0] != 0:
    for i in range(0,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)
    
    
    
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = list(map(int, input().split()))
ans = 0
flag = 0
if n % 2 == 1:
  if a.count(0) != 1: flag = 1
  else:
    sa = n-1
    while sa > 0:
      if a.count(sa) != 2:
        flag = 1
        break
      sa -= 2
else:
  if a.count(0) != 0: flag = 1
  else:
    sa = n-1
    while sa > 0:
      if a.count(sa) != 2:
        flag = 1
        break
      sa -= 2

if flag == 0:
  print(2 ** (n // 2))
else:
  print(0)

Fixed submission:
import math
N = int(input())


A = list(map(int, input().split()))

A.sort()
ans = 0
flag = True
if N % 2 == 1:
  # 0,2,2,4,4,～みたいに並んでるはず
  if A[0] == 0:
    for i in range(1,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)

else:
  if A[0] != 0:
    for i in range(0,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)
    
    
    
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = list(map(int, input().split()))
ans = 0
flag = 0
if n % 2 == 1:
  if a.count(0) != 1: flag = 1
  else:
    for i in range(n // 2 + 1):
      if a[i] != 0 and a.count(a[i]) != 2:
        flag = 1
else:
  if a.count(0) != 0: flag = 1
  else:
    for i in range(n // 2 + 1):
      if a.count(a[i]) != 2:
        flag = 1

if flag == 0:
  print(2 ** (n // 2))
else:
  print(0)

Fixed submission:
import math
N = int(input())


A = list(map(int, input().split()))

A.sort()
ans = 0
flag = True
if N % 2 == 1:
  # 0,2,2,4,4,～みたいに並んでるはず
  if A[0] == 0:
    for i in range(1,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)

else:
  if A[0] != 0:
    for i in range(0,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)
    
    
    
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = list(map(int, input().split()))
ans = 0
flag = 0
if n % 2 == 1:
  if a.count(0) != 1: flag = 1
  else:
    for i in range(n):
      if a[i] != 0 and a.count(a[i]) != 2:
        flag = 1
else:
  if a.count(0) != 0: flag = 1
  else:
    for i in range(n):
      if a.count(a[i]) != 2:
        flag = 1

if flag == 0:
  print(2 ** (n // 2))
else:
  print(0)

Fixed submission:
import math
N = int(input())


A = list(map(int, input().split()))

A.sort()
ans = 0
flag = True
if N % 2 == 1:
  # 0,2,2,4,4,～みたいに並んでるはず
  if A[0] == 0:
    for i in range(1,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)

else:
  if A[0] != 0:
    for i in range(0,N,2):
      if A[i] != i+1 or A[i+1] != i+1:
        flag = False
        break
  
    if flag: ans = 2**(N//2) % (10**9 + 7)
    
    
    
print(ans)