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interview_cake/math/recursive_per.py

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+#!/bin/python
+
+"""
+Write a recursive function for generating all permutations of an input string. Return them as a set.
+"""
+
+def get_permutations(string):
+
+    if len(string) < 2:
+        return set([string])
+
+    all_chars_except_last = string[:-1]
+    last_char = string[-1]
+
+    permutations_of_all_chars_except_last = get_permutations(all_chars_except_last)
+
+    permutations = set()
+    for permutation_of_all_chars_except_last in permutations_of_all_chars_except_last:
+        for position in range(len(all_chars_except_last) + 1):
+            permutation = (
+                permutation_of_all_chars_except_last[:position]
+                + last_char
+                + permutation_of_all_chars_except_last[position:]
+            )
+            permutations.add(permutation)
+
+    
+    return permutations
+
+
+str = "abcd"
+print get_permutations(str)