Submission #1627519

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Source Code Expand

N = input()
src = map(int, raw_input().split())

MOD = 10**9+7

def mul(a,b):
  return (a*b) % MOD

def pow(a,n):
  m = a
  ret = 1
  while n > 0:
    if n%2 == 1:
      ret = mul(ret, m)
    m = mul(m, m)
    n >>= 1
  return ret

def inv(a):
  return pow(a,MOD-2)

def ncr(n,r):
  m = d = 1
  for i in range(r):
    m = mul(m, n-i)
    d = mul(d, i+1)
  return mul(m, inv(d))

ans = 1
seq = 0
for i in range(1,N):
  if src[i] == -1:
    seq += 1
  else:
    if seq > 0:
      a = src[i] - src[i-seq-1]
      ans = mul(ans, ncr(a+seq,seq))
      seq = 0
print ans

Submission Info

Judge Result