Problem-113.py 文件源码

def non_increasing(n_digit=100):
    # a decreasing number can be obtained by reversing an increasing number
    # to consider possible tailing zeros of a decreasing number, I dissect
    # leading part of the coded binary strings into several cases:
    # 0, 10, 110, 1110, 11110, ...
    r = 8
    ori = n_digit + 8
    m = 1
    total = 0
    while ori >= 9:
        cur = factorial(ori) / factorial(r) / factorial(ori-r)
        total += (cur*m)
        m += 1
        ori -= 1

    return total