Buggy python submission (verdict: Runtime Error):
a=list(map(int,input().split()))
if n%2==0:
    b=sorted(a)
    i=0
    while i<len(b):
        if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
            print(0)
            exit()
        i+=2
    print((2**(len(b)//2))%(10**9+7))
else:
    b=sorted(a)
    if len(b)>1:
        if b[1]==0:
            print(0)
            exit()
    if b[0]!=0:
        print(0)
        exit()
    else:
        i=1
        while i<len(b):
            if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
                print(0)
                exit()
            i+=2
        print(2**(len(b)//2)%(10**9+7))



Fixed submission:
n=int(input())
a=list(map(int,input().split()))
if n%2==0:
    b=sorted(a)
    i=0
    while i<len(b):
        if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
            print(0)
            exit()
        i+=2
    print((2**(len(b)//2))%(10**9+7))
else:
    b=sorted(a)
    if len(b)>1:
        if b[1]==0:
            print(0)
            exit()
    if b[0]!=0:
        print(0)
        exit()
    else:
        i=1
        while i<len(b):
            if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
                print(0)
                exit()
            i+=2
        print(2**(len(b)//2)%(10**9+7))

Buggy python submission (verdict: Runtime Error):
n=int(input())
a=list(map(int,input().split()))
if n%2==0:
    b=sorted(a)
    i=0
    while i<len(b)-2:
        if b[i]!=b[i+1] or b[i+2]!=b[i]+2:
            print(0)
            exit()
        i+=2
    print((2**(len(b)//2))%(10**9+7))
else:
    b=sorted(a)
    if b[0]!=0 or b[1]==0:
        print(0)
        exit()
    else:
        i=1
        while i<len(b)-2:
            if b[i]!=b[i+1] or b[i+2]!=b[i]+2:
                print(0)
                exit()
            i+=2
        print(2**(len(b)//2)%(10**9+7))



Fixed submission:
n=int(input())
a=list(map(int,input().split()))
if n%2==0:
    b=sorted(a)
    i=0
    while i<len(b):
        if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
            print(0)
            exit()
        i+=2
    print((2**(len(b)//2))%(10**9+7))
else:
    b=sorted(a)
    if len(b)>1:
        if b[1]==0:
            print(0)
            exit()
    if b[0]!=0:
        print(0)
        exit()
    else:
        i=1
        while i<len(b):
            if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
                print(0)
                exit()
            i+=2
        print(2**(len(b)//2)%(10**9+7))

Buggy python submission (verdict: Runtime Error):
n=int(input())
a=list(map(int,input().split()))
if n%2==0:
    b=sorted(a)
    i=0
    while i<len(b)-2:
        if b[i]!=b[i+1] or b[i+2]!=b[i]+2:
            print(0)
            exit()
        i+=2
    if b[-1]!=b[-2]:
        print(0)
        exit()
    print((2**(len(b)//2))%(10**9+7))
else:
    b=sorted(a)
    if b[0]!=0:
        print(0)
        exit()
    else:
        i=1
        while i<len(b)-2:
            if b[i]!=b[i+1] or b[i+2]!=b[i]+2:
                print(0)
                exit()
            i+=2
        if b[-1]!=b[-2]:
            print(0)
            exit()
        print(2**(len(b)//2)%(10**9+7))




Fixed submission:
n=int(input())
a=list(map(int,input().split()))
if n%2==0:
    b=sorted(a)
    i=0
    while i<len(b):
        if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
            print(0)
            exit()
        i+=2
    print((2**(len(b)//2))%(10**9+7))
else:
    b=sorted(a)
    if len(b)>1:
        if b[1]==0:
            print(0)
            exit()
    if b[0]!=0:
        print(0)
        exit()
    else:
        i=1
        while i<len(b):
            if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
                print(0)
                exit()
            i+=2
        print(2**(len(b)//2)%(10**9+7))

Buggy python submission (verdict: Runtime Error):
n=int(input())
a=list(map(int,input().split()))
if n%2==0:
    b=sorted(a)
    i=0
    while i<len(b):
        if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
            print(0)
            exit()
        i+=2
    print((2**(len(b)//2))%(10**9+7))
else:
    b=sorted(a)
    if b[0]!=0:
        print(0)
        exit()
    else:
        i=1
        while i<len(b):
            if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
                print(0)
                exit()
            i+=2
        print(2**(len(b)//2)%(10**9+7))


Fixed submission:
n=int(input())
a=list(map(int,input().split()))
if n%2==0:
    b=sorted(a)
    i=0
    while i<len(b):
        if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
            print(0)
            exit()
        i+=2
    print((2**(len(b)//2))%(10**9+7))
else:
    b=sorted(a)
    if len(b)>1:
        if b[1]==0:
            print(0)
            exit()
    if b[0]!=0:
        print(0)
        exit()
    else:
        i=1
        while i<len(b):
            if not (b[i]==b[i+1] or b[i+2]==b[i]+2):
                print(0)
                exit()
            i+=2
        print(2**(len(b)//2)%(10**9+7))