Submission #820013

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Source Code Expand

h, w, a, b = map(int, raw_input().split())
mod = 10**9+7
ans = 0
mod_fact = [1]
for i in range(1,h+w-2):
    mod_fact.append((i*mod_fact[i-1])%mod)
factinv = [1] * (h+w-2)
factinv[h+w-3] = pow(mod_fact[h+w-3],(mod-2),mod)
for i in reversed(range(2,h+w-3)):
    factinv[i] = (factinv[i+1] * (i+1))%mod
def C(n,r):
    return mod_fact[n]*factinv[r]*factinv[n-r]%mod
for i in range(b,w):
    ans += C(i+h-a-1,h-a-1) * C(a-1+w-i-1,a-1) % mod
print ans

Submission Info

Judge Result