Submission #7069898

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Source Code Expand

n, d = map(int, input().split())
x, y = map(int, input().split())


def cb(a, b):
    fact = 1
    for i in range(a, a- b, -1):
        fact *= i


    divisor = 1
    for j in range(1, b + 1):
        divisor *= j


    return fact // divisor


if x % d or y % d:
    print(0)


else:
    x_cnt = x // d
    y_cnt = y // d
    ret = 0
    total = (1 / 4) ** n
    if n - y_cnt - x_cnt < 0:
        print(0)
    else:
        remain = n - y_cnt - x_cnt
        if remain % 2:
            print(0)
        else:
            for i in range(0, remain + 1, 2):
                x2 = x_cnt + i
                y2 = n - x_cnt - i
                ret += cb(n, x2) * cb(x2, (x2 + x_cnt) // 2) * cb(y2, (y2 + y_cnt) // 2)
            print(total * ret)

Submission Info

Judge Result