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- def main():
- R = 10**9+7
- N = int(input())
- a = list(map(int, input().split(" ")))
- if a[0] != 0:
- return 0
- amax = max(a)
- h = [0] * (amax+1)
- for i in a:
- h[i] += 1
- if h[0] != 1:
- return 0
- ans = 1
- b = 1
- for i in h[1:]:
- if i == 0:
- return 0
- ans *= pow(2, i * (i - 1) // 2, R)
- ans %= R
- ans *= pow(pow(2, b, R) - 1, i, R)
- ans %= R
- b = i
- return ans
- if __name__ == '__main__':
- print(main())
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