Submission #2699880

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Source Code Expand

N, A, B, K = map(int, input().split())
mod = 998244353

# 階乗 & 逆元計算
factorial = [1]
inverse = [1]
for i in range(1, N+2):
    factorial.append(factorial[-1] * i % mod)
    inverse.append(pow(factorial[-1], mod-2, mod))


# 組み合わせ計算
def nCr(n, r):
    if n < r or r < 0:
        return 0
    elif r == 0:
        return 1
    return factorial[n] * inverse[r] * inverse[n - r] % mod


ans = 0
for x in range(N+1):
    y = (K-A*x)/B
    if y.is_integer():
        ans += nCr(N, x) * nCr(N, int(y)) % mod

print(ans % mod)

Submission Info

Judge Result