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Dynamic Programming in Python: Optimizing Programs for Efficiency

Solution Review: Find All Permutations of a String

In this lesson, we will review the solution to the challenge from the previous lesson.

We'll cover the following...

Solution #

Python 3.5
def permutations(str):
  if str == "": # base case
    return [""]
  permutes = []
  for char in str:
    subpermutes = permutations(str.replace(char, "", 1))    # recursive step
    for each in subpermutes:
      permutes.append(char+each)
  return permutes
def main():
  print (permutations("abc"))
main()

Explanation

Just as we learned in previous lessons, the key to acing recursion is focusing on one step at a time. Try to think of this problem in this way: you already have every possible arrangement of every possible subsequence of the string ...