Problem:
 Score : 300 points    Problem Statement There are N people, conveniently numbered 1 through N .
They were standing in a row yesterday, but now they are unsure of the order in which they were standing.
However, each person remembered the following fact: the absolute difference of the number of the people who were standing to the left of that person, and the number of the people who were standing to the right of that person.
According to their reports, the difference above for person i is A_i .  Based on these reports, find the number of the possible orders in which they were standing.
Since it can be extremely large, print the answer modulo 10^9+7 .
Note that the reports may be incorrect and thus there may be no consistent order.
In such a case, print 0 .      Constraints  1≦N≦10^5  0≦A_i≦N-1         Input The input is given from Standard Input in the following format:  N  A_1  A_2  ...  A_N       Output Print the number of the possible orders in which they were standing, modulo 10^9+7 .        Sample Input 1 5
2 4 4 0 2      Sample Output 1 4  There are four possible orders, as follows:   2,1,4,5,3  2,5,4,1,3  3,1,4,5,2  3,5,4,1,2        Sample Input 2 7
6 4 0 2 4 0 2      Sample Output 2 0  Any order would be inconsistent with the reports, thus the answer is 0 .       Sample Input 3 8
7 5 1 1 7 3 5 3      Sample Output 3 16

Solution (Python):
characteristic=10**9+7
def plus(input1,input2):
    return (input1+input1)%characteristic
def minus(input1,input2):
    return (input1-input2)%characteristic
def times(input1,input2):
    return (input1*input2)%characteristic
def exponen(input1,input2):
    binaryl=list(str(bin(input2))[2:])
    binarysize=len(binaryl)
    binarylist=[int(binaryl[binarysize-1-i]) for i in range(binarysize)]
    modlist=[0 for i in range(binarysize)]
    modlist[0]=input1
    for i in range(1,binarysize):
        modlist[i]=times(modlist[i-1],modlist[i-1])
    answer=1
    for i in range(binarysize):
        if binarylist[i]==1:
            answer=times(answer,modlist[i])
    return answer
def divide(input1,input2):
    return times(input1,exponen(input2,characteristic-2))
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)


B=[]
for i in range(N//2):
    for p in [0,1]:
        B.append(N-1-2*i)
if N%2==1:
    B.append(0)
for i in range(N):
    if A[i]!=B[i]:
        print(0)
        exit()
print(exponen(2,N//2))

Solution (Python):
n = int(input())
l = list(map(int, input().split()))
mod = 10**9 + 7
def f():
  memo = {}

  for i in l:
    if i in memo:
      memo[i] += 1
    else:
      memo[i] = 1
  
  for k, v in memo.items():
    if k == 0 and not v == 1:
      return 0
    elif not k == 0 and not v == 2:
      return 0
  
  return 2**(n//2) % mod

print(f())

Solution (Python):





if __name__ == '__main__':
    from collections import Counter

    person_count = int(input())
    relative_positions = Counter(map(int, input().split()))

    if person_count % 2 == 0:
        for key, value in relative_positions.items():
            if (key % 2 == 0) or (value != 2):
                print(0)
                exit()
    else:
        for key, value in relative_positions.items():
            if (key % 2 == 1) or (key == 0 and value != 1) or (key != 0 and value != 2):
                print(0)
                exit()

    print(2 ** (person_count // 2) % (10 ** 9 + 7))

Solution (Python):
N = int(input())
inline = list(map(int,input().split()))
di = {}
key = 0
if N%2 ==1:
    cen = 0
else:
    cen = -1

for l in inline:
    if l in di:
        if l != cen:
            if di[l] >= 2:
                key += 1
                break
            else:
                di[l] += 1
        else:
            if di[l] >= 1:
                key += 1
                break
    else:
        di[l] = 1

if key >= 1:
    print(0)
else:
    print((2**int(N/2)%(10**9+7)))

Solution (Python):
n=int(input())
a=sorted(list(map(int,input().split())))
flag=True
if n%2==1:
    if a.count(0)!=1:
        flag=False
    for i in range(2,n,2):
        if not (a[i-1]==a[i] and a[i]==i):
            flag=False
            break
else:
    for i in range(1,n,2):
        if not (a[i-1]==a[i] and a[i]==i):
            flag=False
            break
print(2**(n//2)%(10**9+7) if flag else 0)

Solution (Python):
import collections
n = int(input())
a = [int(i) for i in input().split()]
c = collections.Counter(a)
if n%2==0:
	if all(c[i]==2 for i in range(1,n+1,2)):
		answer = (2**(n//2))%(10**9+7)
	else: answer = 0
else:
	if all(c[i]==2 for i in range(2,n+1,2)) and c[0]==1:
		answer = (2**((n-1)//2))%(10**9+7)
	else: answer = 0
print(answer)

Solution (Python):
from collections import Counter

def orders(count, n):
    c = 1
    for k, v in count.items():
        if k == 0:
            if (n % 2 == 0 or v != 1):
                return 0
        elif (n - 1 - k) % 2 == 1 or v != 2:
            return 0
        else:
            c *= v
    return(c % (10 ** 9 + 7))


if __name__ == '__main__':
    n = int(input())
    count = Counter(map(int, input().split()))
    print(orders(count, n))

Solution (Python):
n = int(input())
a = [int(x) for x in input().split()]
d = {}
for x in a:
	d[x] = d.get(x, 0) + 1
ok = True
for i in range(1 + n % 2, n, 2):
	if i not in d or d[i] != 2:
		ok = False
		break
if ok: print(pow(2, n//2, 10**9+7))
else: print(0)

Solution (Python):
n =int(input())
num = [0]*n
tmp = input().split()
L = pow(10,9)+7
for x in range(n):
  num[x] = int(tmp[x])
num.sort()
judge = 1
flg = True
if n%2 == 1:
  judge = 0
  if num[0] != 0:
    flg = False
  else:
    num.pop(0)
prev = -1
count = 0
for i in range(len(num)):
  if prev < 0:
    prev = num[i]
    count += 1
  else:
    if prev == num[i]:
      count += 1
      if count > 2:
        flg = False
        break
    else:
      if count < 2:
        flg = False
        break
      else:
        prev = num[i]
        count = 1
if flg:
  if n%2:
  	print(pow(2,(n-1)//2)%L)
  else:
    print(pow(2,n//2)%L)
else:
  print(0)

Solution (Python):
N = int(input())
A = list(map(int,input().split(" ")))

A.sort(reverse=True)
l = len(A)

if l % 2 == 1:
	if A[-1] != 0:
		print(0)
	else:
		num = (N-1)
		for i in range(0,N-1,2):
			if not (A[i] == A[i+1] == num):
				print(0)
				exit(0)
			num -= 2

		print((2 ** ((N-1)//2)) % ((10 ** 9)+7))
else:
	num = (N-1)
	for i in range(0,N,2):
		if not (A[i] == A[i+1] == num):
			print(0)
			exit(0)
		num -= 2

	print((2 ** ((N)//2)) % ((10 ** 9)+7))

Solution (Python):
import sys
n=int(input())
a=list(map(int,input().split()))
lis=[0 for i in range(n)]
for i in a:lis[i]+=1
if(1):
  if(lis[0]!=n%2):
    print(0)
    sys.exit()
  num=0
  for i in range(1,n):
    if(i%2==n%2):
      if(lis[i]!=0):
        print(0)
        sys.exit()
    else:
      if(lis[i]!=2):
        print(0)
        sys.exit()
      else:num+=1
  print((2**num)%(10**9+7))

Solution (Python):
from collections import Counter

n = int(input())
A = [i for i in input().split()]
c = Counter(A)
ans = 0

if len(A) % 2 == 0:
    if all(v == 2 for v in c.values()):
        ans = 2**(n//2)
        
else:
    if c['0'] == 1 :
        if len(A) == 1:
            ans = 1
        del c['0']
        if all(v == 2 for v in c.values()):
            ans = 2**((n-1)//2)

print(ans % (10**9+7))

Solution (Python):
mod = 10**9+7
def main():
    n = int(input())
    a = list(map(int,input().split()))
    ret = [0]*n
    for i in a: ret[i] += 1
    
    if n%2==1:
        if ret[0] != 1:
            print(0)
            return 0
        for i in range(1,n):
            if i%2==0 and ret[i] != 2 or i%2==1 and ret[i] != 0:
                print(0)
                break
        else:
            print(pow(2,n//2,mod))
    else:
        for i in range(n):
            if i%2==0 and ret[i] != 0 or i%2==1 and ret[i] != 2:
                print(0)
                break
        else:
            print(pow(2,n//2,mod))

main()

Solution (Python):
def c_LiningUp(N, A):
    MOD = 10**9 + 7
    A = sorted(A)
    if N % 2 == 0:
        
        
        B = [i for i in range(1, N, 2)]
        B = sorted(B + B)
    else:
        
        
        B = [i for i in range(2, N, 2)]
        B = sorted([0] + B + B)
    if A == B:
        return 2**(N // 2) % MOD  
    else:
        return 0
    return None

N = int(input())
A = [int(i) for i in input().split()]
print(c_LiningUp(N, A))

Solution (Python):
from collections import Counter
N = int(input())
A = sorted(list(map(int, input().split())))
div = 10 ** 9 + 7
if N % 2 == 0:
    B = [i for i in range(1, N, 2)]
    B.extend(B)
    B.sort()
    if A == B:
        print(2**(int(N/2)) % div)
    else:
        print(0)

else:
    B = [i for i in range(2, N, 2)]
    B.extend(B)
    B.append(0)
    B.sort()
    if A == B:
        print(2**(int(N/2)) % div)
    else:
        print(0)

Solution (Python):
from collections import defaultdict, Counter


def main():
    N = int(input())
    A = map(int, input().split())

    ans = AC(N, A)
    print(ans)


def AC(N, A):
    """
    差分のとり方を用意しておく
    報告に問題があるか調べる
    差分のとり方＝組合せの要素になる
    """
    diff_dict = defaultdict(int)
    for i in range(1, N + 1):
        left, right = i - 1, N - i
        diff = abs(left - right)
        diff_dict[diff] += 1

    c = Counter(A)
    if diff_dict != c:
        return 0

    ans = 1
    for count in c.values():
        ans = (ans * count) % (10 ** 9 + 7)

    return ans

if __name__ == '__main__':
    main()

Solution (Python):
N=input()
a=map(int,raw_input().split())



b=[]
for i in range(1,N+1):
	b.append( abs((N-i)-(i-1)) )



a.sort()
b.sort()
if a != b:
	print 0
else:
	k=len(a)/2
	print 2**k%(10**9+7)

Solution (Python):
num =int(input())

val = [int(x) for x in input().split()]

_len = len(val)
sort_val = sorted(val)
res = False

if len(sort_val) %2 == 0:
    tmp = sort_val[1::2]
    tmp2 = sort_val[::2]
    if sorted(tmp) == sorted(tmp2):
        res = True
else:
    if sort_val.count(0) != 1:
        pass
    else:
        del sort_val[0]
        tmp = sort_val[::2]
        tmp2 = sort_val[1::2]
        if sorted(tmp) == sorted(tmp2):
            res = True

cnt = 1
if res:
    for i in range(0, _len//2):
        cnt = cnt*2 % 1000000007

print(0 if not res else cnt)

Solution (Python):



"""050-c"""

import sys
import pprint
import re

import itertools
pp = pprint.PrettyPrinter(indent=2)

mod = 1000000007

def main():
    """Main function."""
    N = int(input())
    as_ = sorted(list(map(int, input().split(' '))), reverse=True)

    checker = N - 1
    if N % 2 != 0:
        if as_[-1] != 0:
            print(0)
            sys.exit(0)
        else:
            N = N - 1

    for i in range(0, N, 2):
        if as_[i] != checker or as_[i + 1] != checker:
            print(0)
            sys.exit(0)
        checker = checker - 2

    print(pow(2, N // 2, mod))

if __name__ == '__main__':
    sys.exit(main())

Solution (Python):
import sys

n = int(input())
a = list(sorted(map(int, input().split())))
M = 10**9 + 7

end = lambda x: print(x) or sys.exit()
result = 1
n2 = n % 2
if n2 == a[0] % 2:
    end(0)
tmp = None
if n2:
    if a[0]:
        end(0)
else:
    if not a[0] == a[1] == 1:
        end(0)
for a1, a2 in zip(a[n2::2], a[n2 + 1::2]):
    if a1 - a2:
        end(0)
    if tmp:
        if a1 - tmp - 2:
            end(0)

    tmp = a1
    result *= 2
    if result >= M:
        result %= M
end(result)

Solution (Python):


from collections import Counter


def solve():
    while 1:
        try:
            N = int(input())
            A = list(map(int, input().split(" ")))
            MOD = 10 ** 9 + 7
            counter = Counter(A)
            checker = [0 for _ in range(N)]
            for word, cnt in counter.most_common():
                if word > N - 1 or cnt > 2:
                    raise EndLoop
                else:
                    checker[word] = cnt

            if N % 2 == 0:
                for i in range(N):
                    if not i % 2 and checker[i] != 0:
                        raise EndLoop
                    elif i % 2 and checker[i] != 2:
                        raise EndLoop

                print((2 ** (N // 2)) % MOD)
                break
            else:
                for i in range(N):
                    if i == 0 and checker[i] != 1:
                        raise EndLoop
                    elif not i % 2 and i != 0and checker[i] != 2:
                        raise EndLoop
                    elif i % 2 and checker[i] != 0:
                        raise EndLoop

                print(((2 ** ((N - 1) // 2)) % MOD))
                break
        except:
            print(0)
            break


solve()

Solution (Python):
def end():
    print(0)
    exit()


n = int(input())
a = list(map(int, input().split()))

b = [0] * ((n + 1) // 2)

if n % 2 == 0:
    for x in a:
        if x % 2 == 0:
            end()
        b[x // 2] += 1
    for y in b:
        if y != 2:
            end()
else:
    for x in a:
        if x % 2 != 0:
            end()
        b[x // 2] += 1
    for y in b[1:]:
        if y != 2:
            end()
        if b[0] != 1:
            end()

print((2 ** (n // 2) % (10 ** 9 + 7)))

Solution (Python):
n = int(input())
a = list(map(int, input().split()))

b = [0] * ((n + 1) // 2)

if n % 2 == 0:
    for x in a:
        if x % 2 == 0:
            print(0)
            exit()
        b[x // 2] += 1
    for y in b:
        if y != 2:
            print(0)
            exit()
else:
    for x in a:
        if x % 2 != 0:
            print(0)
            exit()
        b[x // 2] += 1
    for y in b[1:]:
        if y != 2:
            print(0)
            exit()
        if b[0] != 1:
            print(0)
            exit()

print((2 ** (n//2)%(10**9+7)))

Solution (Python):
N = int(input())
A = [int(i) for i in input().split()]
mod = 10 ** 9 + 7
A.sort()


def solve(i, num):
    while i < len(A):
        if A[i] == num:
            if A[i + 1] == num:
                i += 2
                num += 2
            else:
                break
        else:
            break
    if i >= len(A):
        print(2 ** (N // 2) % mod)
    else:
        print(0)


if len(A) % 2 is 0:
    solve(0, 1)
else:
    if A[0] is 0:
        solve(1, 2)
    else:
        print(0)

Solution (Python):
from collections import Counter
N = int(input())
listA = input().split()

if N % 2 == 1:
    count = Counter(listA)
    i = 0
    flag = True
    while i < N:
        if i == 0 and count[str(i)] == 1:
            i = i + 2
            continue
        elif count[str(i)] == 2:
            i = i + 2
            continue
        else:
            flag = False
            break
    if flag:
        print((2 ** ((N-1)//2)) % (10**9 + 7))
    else:
        print("0")
else:
    count = Counter(listA)
    i = 1
    flag = True
    while i < N:
        if count[str(i)] == 2:
            i = i + 2
            continue
        else:
            flag = False
            break
    if flag:
        print(2 ** (N//2) % (10**9 + 7))
    else:
        print("0")

Solution (Python):
INF = 10**9+7

N = int(input())
A = sorted( list(map(int,input().split())) )
if N%2==1:
    tmp = [ 2*j for j in range(1,N//2+1)]
    TMP = sorted([0]+tmp+tmp)
else:
    tmp = [2*j+1 for j in range(N//2)]
    TMP = sorted(tmp+tmp)
if A==TMP:
    tmp=1
    for _ in range(N//2):
         tmp *=2
         tmp %=INF
    print(tmp)
else:
    print(0)

Solution (Python):
mod=10**9+7
n=int(input())
l=[int(x) for x in input().split()]
f=[0]*(10**5)
for ele in l:
    f[ele]+=1
if n%2==0 and f[0]:
    print(0)
elif f[0]>1:
    print(0)
else:
    cnt=0
    for i in range(1,n):
        if f[i]:
            cnt+=1
        if f[i]>2:
            print(0)
            break
    else:
        print(pow(2,cnt,mod))

Solution (Python):
import sys
from collections import Counter

M = 10 ** 9 + 7





def read_int_list():
    return list(map(int, input().split()))


def read_str_list():
    return input().split()


def read_int():
    return int(input())


def read_str():
    return input()


def solve():
    n = read_int()
    a = read_int_list()

    c = Counter(a)
    expected = Counter()
    if n % 2 == 0:
        for i in range(1, n, 2):
            expected[i] = 2
    else:
        expected[0] = 1
        for i in range(2, n, 2):
            expected[i] = 2

    if c == expected:
        return 2 ** (n // 2) % M
        
    return 0


def main():
    res = solve()
    print(res)


main()

Solution (Python):
import sys
from collections import Counter

M = 10 ** 9 + 7




def read_int_list():
    return list(map(int, input().split()))


def read_str_list():
    return input().split()


def read_int():
    return int(input())


def read_str():
    return input()


def solve():
    n = read_int()
    a = read_int_list()

    c = Counter(a)
    expected = Counter()
    if n % 2 == 0:
        for i in range(1, n, 2):
            expected[i] = 2
    else:
        expected[0] = 1
        for i in range(2, n, 2):
            expected[i] = 2

    if c == expected:
        return pow(2, n // 2, M)
    return 0


def main():
    res = solve()
    print(res)


main()

Solution (Python):
from collections import defaultdict
from collections import Counter

MOD = 10 ** 9 + 7
def main():
    N = int(input())
    c = Counter(list(map(int, input().split())))

    if N % 2 == 0 and c[0] != 0:
        print(0)
        return
    if N % 2 != 0 and c[0] != 1:
        print(0)
        return
    for i in range(N - 1, 0, -2):
        if c[i] != 2:
            print(0)
            return

    print(pow(2, (N // 2), MOD))

if __name__ == '__main__':
    main()

Solution (Python):
from collections import Counter

N = input()
A = map(int, raw_input().split())
hist = Counter(A)

def valid():
  if N % 2 == 0:
    for i in range(1,N,2):
      if hist[i] != 2:
        return False
    return True
  else:
    if hist[0] != 1:
      return False
    for i in range(2,N,2):
      if hist[i] != 2:
        return False
    return True

if valid():
  a = N/2
  print 2**a % (10**9+7)
else :
  print 0

Solution (Python):
N = int(raw_input())
A = sorted(map(int, raw_input().split()))
ans = 1
for i in range(N):
    if A[i] == 2*((i + N%2) / 2) + (1 - N % 2):
        if i % 2 == 1:
            ans = (ans * 2) % (10**9 + 7)
    else:
        ans = 0
        break
print ans

Solution (Python):


n = input()
a = map(int,raw_input().split())

mod = 10**9+7
flg = [False]*n
      
for i in range(n):
    if(flg[a[i]]==False):
        flg[a[i]] = True
    elif(flg[a[i]-1]==False and a[i]-1>=0):
        flg[a[i]-1] = True
    
           
if(n%2==0):
    if(all(flg)):
        print(2**(n/2) % mod)
    else:
        print('0')
else:
    if(all(flg)):
        print(2**((n-1)/2) % mod)
    else:
        print('0')

Solution (Python):
from collections import Counter

n = int(raw_input())
ct = Counter(map(int, raw_input().split()))
correct = True
for i,j in zip(ct.keys(), ct.values()):
    if (n % 2) == (i % 2):
        correct = False
    elif i >= n:
        correct = False
    elif i == 0:
        if j != 1:
            correct = False
    else:
        if j != 2:
            correct = False
if correct:
    print (2**(n/2)) % (10**9+7)
else:
    print 0

Solution (Python):
import copy
n = int(input())
a = list(map(int, input().split()))
a.sort()
flag = True
if n % 2 == 1:
    if a[0] != 0:
        print(0)
    else:
        ans = [i for i in range(2, n, 2) for j in range(2)]
        ans.insert(0, 0)
        if ans != a:
            print(0)
            flag = False
    if flag:
        print((2**((n - 1) // 2)) % (10**9 + 7))

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

Solution (Python):
def main():
    N = int(input())
    A = list(map(int, input().split()))

    a = list(range(N))
    if N % 2 == 1:
        a2 = a[::2] * 2
        a2.sort(reverse=True)
        a2.pop()
    else:
        a2 = a[1::2] * 2
        a2.sort(reverse=True)
    A.sort(reverse=True)

    if tuple(a2) == tuple(A):
        comb = (2 ** (N // 2)) % 1000000007
        print(str(comb))
    else:
        print('0')

main()

Solution (Python):
def main():
    N = int(input())
    A = list(map(int, input().split()))

    if N % 2 == 1:
        A.append(0)

    A.sort()
    ev = tuple(A[::2])
    od = tuple(A[1::2])

    if ev == od:
        comb = (2 ** (N // 2)) % 1000000007
        print(str(comb))
    else:
        print('0')

main()

Solution (Python):
num = int(raw_input())
array = map(int, raw_input().split(" "))

a = sorted(array)

if num % 2 == 0:
    for i in xrange(0, num, 2):
        if a[i] != a[i + 1]:
            print 0
            break
    else:
        div = pow(10, 9) + 7
        print pow(2, num / 2) % div
else:
    for i in xrange(1, num, 2):
        if a[i] != a[i + 1]:
            print 0
            break
    else:
        div = pow(10, 9) + 7
        print pow(2, num / 2) % div

Solution (Python):
N = int(input())

seq = [int(i) for i in input().split()]
seq_sort = sorted(seq)

if N % 2 == 0:
    seq_even = []
    for i in range(N // 2):
        seq_even += [2 * i + 1, 2 * i + 1]
    if seq_sort == seq_even:
        print((2 ** (N // 2)) % (10 ** 9 + 7))
    else:
        print(0)
else:
    seq_odd = [0]
    for i in range(N // 2):
        seq_odd += [2 * (i + 1), 2 * (i + 1)]
    if seq_sort == seq_odd:
        print((2 ** (N // 2)) % (10 ** 9 + 7))
    else:
        print(0)

Solution (Python):
n = int(input())
a = [int(x) for x in input().split()]

def is_satisfied(s):
    ln = len(s)
    check = sorted(list(range(ln - 1, 1, -2)) * 2)
    if ln % 2 == 0:
        check.insert(0, 1)
        check.insert(0, 1)
    else:
        check.insert(0, 0)

    return sorted(s) == check

    
    
    
    
    
    
    
    
    

    


ans = 2 ** (n // 2) % (10 ** 9 + 7)
print(ans if is_satisfied(a) else 0)

Solution (Python):
N=int(input())
A=[int(n) for n in input().split()]
import sys

div=10**9+7

A.sort()

if N % 2 == 0:
    for i in range(int(N/2)):
        if A[2*i] != 2*i+1 or A[2*i+1] != 2*i+1:
            print (0)
            sys.exit() 
    print(2**int(N/2) % div)
if N % 2 == 1:
    if A[0]!=0:
        print(0)
        sys.exit()
    for i in range(int((N-1)/2)):
        if A[2*i+1] !=2*i+2  or A[2*i+2]!= 2*i+2:
            print(0)
            sys.exit()
    print(2**int((N-1)/2) % div)

Solution (Python):
N = int(input())
A = list(map(int,input().split()))
Nc = 0
e = 0
A.sort()
if N % 2 == 0:
    B = [2*i - 1 for i in range(1, N//2 + 1)]
    B = B + B
    B.sort()
    if A == B:
        Nc = 2**(N//2)
else:
    B = [2*i for i in range(1, (N-1)//2 + 1)]
    B = B + B + [0]
    B.sort()
    if A == B:
        Nc = 2**((N-1)//2)

print(Nc%1000000007)

Solution (Python):
N = int(input())
A = list(map(int,input().split()))
Nc = 1
e = 0
B = [0]*N
for i in A:
    if (N-i-1) < 0:
        e = 1
        Nc = 0
        break
if e ==0:
    if A.count(0) >= 2:
        Nc *= 0
    else:
        if A.count(0) == 1:
            A.remove(0)
        for i in A:
            B[i] = B[i] + 1
        for i in B:
            if i == 2:
                Nc *= 2
            elif i == 0:
                Nc *= 1
            else:
                Nc *= 0
                break
print(Nc%1000000007)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))

if N % 2 == 0:
    B = []
    for i in range(int(N/2)):
        B.append(i*2 + 1)
        B.append(i*2 + 1)
else:
    B = [0]
    for i in range(int(N/2)):
        B.append(i*2 + 2)
        B.append(i*2 + 2)

if sorted(A) == B:
    print((2 ** int(N/2)) % (10**9 + 7))
else:
    print(0)

Solution (Python):
n = int(raw_input().strip())
a = map(int, raw_input().strip().split())
a.sort()


def validate(a, n):
	if n & 1 == 0:
		s = 0
		p = 1
	else:
		s = 1
		p = 2
		if a[0] != 0:
			return False
	for i in range(s, n, 2):
		if a[i] != a[i + 1]:
			return False
	return True


if not validate(a, n):
	print 0
else:
	print (1 << (n >> 1)) % int(1e9 + 7)

Solution (Python):
n = input()

a, b = map(int, raw_input().split()), [abs(x - (n - x - 1)) for x in xrange(n)]
a.sort()
b.sort()
if a != b:
	print '0'
	exit(0)

n >>= 1
s, e = 1, 2
MOD = 10 ** 9 + 7
while n > 0:
	if (n & 1) == 1:
		s = s * e % MOD
	e = e * e % MOD
	n >>= 1
print s

Solution (Python):

import sys

n=int(raw_input())
a=map(int,raw_input().split())
b=sorted(a)
if n%2==0:
 for i in xrange(0,n,2):
  if b[i+1]!=b[i]:
   print 0
   sys.exit()
 else:
  print (2**(n/2))%(10**9+7)
else:
 for i in xrange(1,n,2):
  if b[i+1]!=b[i]:
   print 0
   sys.exit()
 else:
  print (2**(n/2))%(10**9+7)

Solution (Python):
n=int(input())
a=list(map(int,input().split()))
b=sorted(a)
if n%2==1:
    b=b[1:]

if n%2==0:
    for i in range(n):
        if b[i] != (i//2)*2+1:
            print(0)
            exit()
    else:
        print(2**(n//2) % (10**9+7))

if n%2==1:
    for i in range(n-1):
        if b[i] != (i//2)*2+2:
            print(0)
            exit()
    else:
        print(2**(n//2) % (10**9+7))

Solution (Python):
from collections import Counter

N = int(input())
A = [int(a) for a in input().split()]
 
check = {}
 
if N % 2 == 0:
    for i in range(1, N, 2):
        check[i] = 2
else:
    check[0] = 1
 
    for i in range(2, N, 2):
        check[i] = 2
 
if check == Counter(A):
    print((2 ** (N // 2)) % (10 ** 9 + 7))
else:
    print(0)

Solution (Python):

N = int(input())
A = [int(a) for a in input().split()]

check = []

if N % 2 == 0:
    for i in range(1, N, 2):
        check += [i, i]
else:
    check += [0]

    for i in range(2, N, 2):
        check += [i, i]

if check == sorted(A):
    print((2 ** (N // 2)) % (10 ** 9 + 7))
else:
    print(0)

Solution (Python):
def solve(n, a_lst):
    dic = {}

    for i in range(1, n + 1, 2):
        j = n - i
        dic[j] = 1 if j == 0 else 2

    for i in a_lst:
        if i not in dic:
            return 0

        dic[i] -= 1

        if dic[i] < 0:
            return 0

    return pow(2, n // 2) % (pow(10, 9) + 7)


if __name__ == '__main__':
    n = int(input())
    a_lst = [int(x) for x in input().split()]
    print(solve(n, a_lst))

Solution (Python):
from collections import Counter

N = int(raw_input())
A = Counter(map(int, raw_input().split()))
cnt = 1
for k, v in A.items():
    if k == 0:
        continue
    if k % 2 == N % 2:
        print 0
        exit()
    if v != 2:
        print 0
        exit()
    cnt *= 2
    cnt %= 10 ** 9 + 7
print cnt

Solution (Python):
N = int(input())
A = list(map(lambda x:int(x), input().split()))

fail=False
count_list = [0]*(int((N-1)/2)+1)
for i in range(N):
	if A[i]%2==N%2:
		print(0)
		fail=True
		break
	count_list[int(A[i]/2)] = count_list[int(A[i]/2)]+1
if not fail:
	if N%2==0:
		for c in count_list:
			if c!=2:
				print(0)
				break
		else:
			result = 2
			for i in range(int(N/2)-1):
				result = result*2%(10**9+7)
			print(result)
	if N%2==1:
		if count_list[0]!=1:
			print(0)
		else:
			count_list.pop(0)
			for c in count_list:
				if c!=2:
					print(0)
					break
			else:
				if N==1:
					print(1)
				else:
					result = 2
					for i in range(int((N-1)/2)-1):
						result = result*2%(10**9+7)
					print(result)

Solution (Python):
class Lining:

    def line(self, N, A):

        if N == 1:
            print 1
            return

        if N == 2:
            print 2
            return

      
        if N % 2:

            m = [0 for i in range((N/2)+1)]
            for a in A:
                idx = a/2
                m[idx] += 1

            if m[0] != 1:
                print 0
                return

            ans = 1
            for i in range(1, (N/2)+1):
                ans *= 2

                if m[i] != 2:
                    print 0
                    return

            print ans % (pow(10, 9) + 7)

        else:

            m = [0 for i in range(N/2)]
            for a in A:
                idx = a/2
                m[idx] += 1

            ans = 1
            for i in range(N/2):
                ans *= 2

                if m[i] != 2:
                    print 0
                    return

            print ans % (pow(10, 9) + 7)

if __name__ == "__main__":

    N = input()
    A = [int(i) for i in raw_input().split()]

    abc = Lining()
    abc.line(N, A)

Solution (Python):
MOD = int(1e9) + 7
N = int(input())
A = list(map(int, input().split()))

A.sort()
ansflag = True
if N % 2 == 0:
	for i in range(N):
		if A[i] != (i // 2) * 2 + 1:
			ansflag = False
			break
else:
	if A[0] != 0:
		ansflag = False
	for i in range(1, N):
		if A[i] != ((i+1) // 2) * 2:
			ansflag = False
			break

if ansflag:
	def repeatSquares(x, n):  
		res = 1
		while n != 0:
			if n % 2 == 1:
				res *= x
				res %= MOD  
			x *= x
			n //= 2
			x %= MOD      
		return res

	print(repeatSquares(2, N // 2))
else:
	print(0)

Solution (Python):
from collections import Counter
N = int(input())
l, m = N%2, N//2
c = Counter([a//2-l for a in map(int, input().split())])
print((1 << m) % (10**9+7) if all(c[i] == 2 for i in range(m)) else 0)

Solution (Python):
N = int(input())
o, h = N%2, N//2
arr = [0]*h
for a in map(int, input().split()):
    if a > 0:
        arr[a//2 - o] += 1
if all(c == 2 for c in arr):
    print((1 << h) % (10**9 + 7))
else:
    print(0)

Solution (Python):

from collections import Counter

def check(n, a):
    count = Counter(a)
    if n % 2 == 1 and (0 not in count or count[0] != 1):
        return False
    for i in range(1 + (n % 2), n+1, 2):
        if i not in count or count[i] !=2:
            return False
    return True

if __name__ == "__main__":
    N = int(input())
    A = list(map(int, input().split()))

    m = N // 2
    if not check(N,A):
        print(0)
    else:
        print((2 ** m) % (10**9+7))

Solution (Python):

from collections import Counter

def check(n, a):
    count = Counter(a)
    if n % 2 == 1 and (0 not in count or count[0] != 1):
        return False
    for i in range(1 + (n % 2), n+1, 2):
        if i not in count or count[i] !=2:
            return False
    return True

if __name__ == "__main__":
    N = int(input())
    A = list(map(int, input().split()))

    if not check(N,A):
        print(0)
    else:
        if N > 1:
            c = 2
            for _ in range((N // 2) - 1):
                c = c * 2 % (int(1e9) + 7)
            print(c)
        else:
            print(1)

Solution (Python):
from collections import Counter


def check(n, a):
    aa = Counter(a)
    if n & 1 and (0 not in aa or aa[0] != 1):
        return False
    for i in range(1 + (n & 1), n + 1, 2):
        if i not in aa or aa[i] != 2:
            return False
    return True


def solve():
    n = int(input())
    a = list(map(int, input().split()))

    if not check(n, a):
        return 0

    exp = n // 2
    if exp < 30:
        return 2 ** exp
    c = 2 ** 29
    d = int(1e9) + 7
    exp -= 29
    for _ in range(exp):
        c = c * 2 % d
    return c


print(solve())

Solution (Python):
MOD = 10**9+7
n = int(input())
xs = list(map(int, input().split()))
cnt = [0 for _ in range(n)]
for x in xs:
    cnt[x] += 1

res = 1
if n % 2 == 0:
    s = 1
else:
    s = 2
    if cnt[0] != 1:
        res = 0
for i in range(s,n,2):
    if cnt[i] != 2:
        res = 0
    res *= 2
    res %= MOD
    
print(res)

Solution (Python):
def detect(n,c):
    if n%2 and c.pop(0) != 1:
        return False
    for i in range(1,n,2):
        if c[i] != 2:
            return False
    else:
        return True

N = int(input())

count = [0 for x in range(N)]
for x in map(int,input().split()):
    count[x] += 1

if detect(N,count):
    print((2**(N>>1)) % 1000000007)
else:
    print(0)