Understanding - Advanced, exercise 22

Text

The variable my_mat_string contains the string of a 10-digit matriculation number (e.g. "0000123456"). Study the execution of the following function when it is called as follows: f(my_mat_string).

def f(m_string):
    t = 0
    cl = list()
    for c in m_string:
        cl.append(int(c))
        t = t + int(c)
    
    eo_value = t % 2 == 0
    cl = on(cl, eo_value)
    idx = t % len(m_string) 
    return cl[idx], cl

def on(ln, flag):
    c_len = len(ln)
    if c_len > 1: 
        if (flag and ln[0] > ln[c_len - 1]) or (not flag and ln[0] < ln[c_len - 1]):
            t = ln[0]
            ln[0] = ln[c_len - 1]
            ln[c_len - 1] = t
        m = c_len // 2
        return on(ln[0:m], flag) + on(ln[m:c_len], flag)
    else:
        return ln

Hints

The function f is organised in two blocks. The first block does a first computation on the input received, while in the second block the computed value is passed to the rescursive function on.

Additional material

The runnable Python file is available online. You can run it executing the command python exercise_22.py in a shell, and then following the instructions on screen to specify the intended input.