MOD = 10 ** 9 + 7 # これがないと計算できない
def cmb_gen(n):
fac = [0] * n
inv = [0] * n
fac[0] = fac[1] = 1
inv[0] = inv[1] = 1
for i in range(2, n):
fac[i] = (fac[i - 1] * i) % MOD
inv[i] = pow(fac[i], MOD - 2, MOD)
def cmb_mod(n, r):
return (fac[n] * inv[n - r] * inv[r]) % MOD
return cmb_mod
N = int(input())
xs = list(map(int, input().split()))
cmb_mod = cmb_gen(N)
r = 0
for i in range(N):
r += xs[i] * cmb_mod(N-1, i)
r %= MOD #<-例えばここでちゃんと割る
print(r)
Last active
May 11, 2019 10:46
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combinationのパターンを計算するやつ
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