Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline

n = int(input())
A = list(map(int, input().split()))
ans = 0
flag = True
nums = {}
for a in A:
    if a not in nums:
        nums[a] = 1
    else:
        nums[a] += 1

if n % 2 == 1:
    if nums[0] != 1:
        flag = False
    for i in range(n//2):
        if nums[2*(i+1)] != 2:
            flag = False
            break
else:
    for i in range(n//2):
        if nums[2*i+1] != 2:
            flag = False
            break

if flag == True:
    ans = 2**(n//2)
    ans = ans % (10**9 + 7)
    
print(ans)

Fixed submission:
n = int(input())
nums = {0:0}

for i in list(map(int, input().split())):
    if i in nums:
        nums[i] += 1
        if nums[i] > 2:
            ans = 0
            break
    else:
        nums[i] = 1
        
if n % 2 == 0:
    if 1 in nums.values():
        ans = 0
    else:
        ans = 2**(n//2)
        
else:
    if nums[0] == 1:
        del nums[0]
        if 1 in nums.values():
            ans = 0
        else:
            ans = 2**((n-1)//2)
    else:
        ans = 0
        
print(ans % (10**9+7))

Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline

n = int(input())
A = list(map(int, input().split()))
ans = 0
flag = True
nums = {}
for a in A:
    if a in nums:
        nums[a] += 1
    else:
        nums[a] = 1

if n % 2 == 1:
    if nums[0] != 1:
        flag = False
    for i in range(n//2):
        if nums[2*(i+1)] != 2:
            flag = False
            break
else:
    for i in range(n//2):
        if nums[2*i+1] != 2:
            flag = False
            break

if flag == True:
    ans = 2**(n//2)
    ans = ans % (10**9 + 7)
    
print(ans)

Fixed submission:
n = int(input())
nums = {0:0}

for i in list(map(int, input().split())):
    if i in nums:
        nums[i] += 1
        if nums[i] > 2:
            ans = 0
            break
    else:
        nums[i] = 1
        
if n % 2 == 0:
    if 1 in nums.values():
        ans = 0
    else:
        ans = 2**(n//2)
        
else:
    if nums[0] == 1:
        del nums[0]
        if 1 in nums.values():
            ans = 0
        else:
            ans = 2**((n-1)//2)
    else:
        ans = 0
        
print(ans % (10**9+7))

Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline

n = int(input())
A = list(map(int, input().split()))
ans = 0
flag = True
nums = {}
for a in A:
    if a in nums:
        nums[a] += 1
    else:
        nums[a] = 1

if n % 2 == 1:
    if nums[0] != 1:
        flag = False
    for i in range(n//2):
        if nums[2*(i+1)] != 2:
            flag = False
            break
else:
    for i in range(n//2):
        if nums[2*i+1] != 2:
            flag = False
            break

if flag == True:
    ans = 2**(n//2) % (10**9 + 7)
    
print(ans)

Fixed submission:
n = int(input())
nums = {0:0}

for i in list(map(int, input().split())):
    if i in nums:
        nums[i] += 1
        if nums[i] > 2:
            ans = 0
            break
    else:
        nums[i] = 1
        
if n % 2 == 0:
    if 1 in nums.values():
        ans = 0
    else:
        ans = 2**(n//2)
        
else:
    if nums[0] == 1:
        del nums[0]
        if 1 in nums.values():
            ans = 0
        else:
            ans = 2**((n-1)//2)
    else:
        ans = 0
        
print(ans % (10**9+7))

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

n = int(input())
A = list(map(int, input().split()))
A.sort()
ans = 0
flag = True

if n % 2 == 1:
    if 0 not in A:
        flag = False
    for i in range(n//2):
        if A.count(2*(i+1)) != 2:
            flag = False
else:
    for i in range(n//2):
        if A.count(2*i + 1) != 2:
            flag = False

if flag == True:
    ans = 2**(n//2) % (10**9 + 7)

print(ans)

Fixed submission:
n = int(input())
nums = {0:0}

for i in list(map(int, input().split())):
    if i in nums:
        nums[i] += 1
        if nums[i] > 2:
            ans = 0
            break
    else:
        nums[i] = 1
        
if n % 2 == 0:
    if 1 in nums.values():
        ans = 0
    else:
        ans = 2**(n//2)
        
else:
    if nums[0] == 1:
        del nums[0]
        if 1 in nums.values():
            ans = 0
        else:
            ans = 2**((n-1)//2)
    else:
        ans = 0
        
print(ans % (10**9+7))

Buggy python submission (verdict: Runtime Error):
n = int(input())
nums = {0:0}

for i in list(map(int, input().split())):
    if i != 0 and (n%2 == i%2):
        print(0)
        break
    if i in nums:
        if nums[i] <= 1:
            nums[i] += 1
        else:
            print(0)
            break
    else:
        nums[i] = 1
else:        
    if n%2 == 1:
        if nums[0] == 0:
            print(0)
            break
    del nums[0]
    
    if 1 in list(nums.values()):
        print(0)
    else:
        print(2**len(nums.values()))


Fixed submission:
n = int(input())
nums = {0:0}

for i in list(map(int, input().split())):
    if i in nums:
        nums[i] += 1
        if nums[i] > 2:
            ans = 0
            break
    else:
        nums[i] = 1
        
if n % 2 == 0:
    if 1 in nums.values():
        ans = 0
    else:
        ans = 2**(n//2)
        
else:
    if nums[0] == 1:
        del nums[0]
        if 1 in nums.values():
            ans = 0
        else:
            ans = 2**((n-1)//2)
    else:
        ans = 0
        
print(ans % (10**9+7))