Average of two strings in alphabetical/lexicographical order

Question

Suppose you take the strings \'a\' and \'z\' and list all the strings that come between them in alphabetical order: [\'a\',\'b\',\'c\' ... \'x\',\'y\',\'z\']. Take the midpoint

Answer 1

I haven't programmed in python in a while and this seemed interesting enough to try. Bear with my recursive programming. Too many functional languages look like python.

def stravg_half(a, ln):
     # If you have a problem it will probably be in here.
     # The floor of the character's value is 0, but you may want something different
     f = 0
     #f = ord('a')
     L = ln - 1
     if 0 == L:
          return ''
     A = ord(a[0])
     return chr(A/2) + stravg_half( a[1:], L)

def stravg_helper(a, b, ln, x):
    L = ln - 1
    A = ord(a[0])
    B = ord(b[0])
    D = (A + B)/2
    if 0 == L:
        if 0 == x:
             return chr(D)
        # NOTE: The caller of helper makes sure that len(a)>=len(b)
        return chr(D) + stravg_half(a[1:], x)
    return chr(D) + stravg_helper(a[1:], b[1:], L, x)

def stravg(a, b):
    la = len(a)
    lb = len(b)
    if 0 == la:
        if 0 == lb:
            return a # which is empty
        return stravg_half(b, lb)
    if 0 == lb:
        return stravg_half(a, la)
    x = la - lb
    if x > 0:
        return stravg_helper(a, b, lb, x)
    return stravg_helper(b, a, la, -x) # Note the order of the args