All Permutations of a String in Python (Recursive)

Question

I need a kick in the head on this one. I have the following recursive function defined:

def perms(s):
  if(len(s)==1):
    return s

  res = \'\'
  for x in          


        

Answer 1

This kind of thing is a nice place for generators (https://docs.python.org/3.3/tutorial/classes.html#generators), and yield.

Try something like this (not tested):

def permute_string(s):
    if len(s) <= 1:   #  "" and 1 char strings are their all their own permutaions.
        yield s
        return

    head = s[0] # we hold on to the first character
    for tail in permute_string(s[1:]) :   # permute the rest
        yield head + tail


# main
for permutation in permute_string(s) :
    print(permutation)

This is the classic permutation algorithm: you keep the first character and prepend it to all permutations of the remaining characters. This particular function is a python generator: that means it can keep running while yielding its results one-by-one. In this case, it makes it easier to concentrate on the algorithm without worrying about the details of how to get the data back to the caller.