🏣 Clean up for arxiv

book/ebook_src/real_interview_problems/combination.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+def combination(array):
+    if len(array) < 2:
+        return set(array)
+    
+    result = set()
+    for index, item in enumerate(array):
+        new_array = array[:index] + array[index+1:]
+        result.add(item)
+        for perm in combination(new_array):
+            new_item = ''.join(sorted(item + perm))
+            result.add(new_item)
+    
+    return result
+    
+    
+    
+if __name__ == '__main__':
+    array = ['a', 'b', 'c']
+    result = set(['a', 'ac', 'ab', 'abc', 'bc', 'c', 'b']) 
+    assert(combination(array) == result)
+    
+    array = ['']
+    result = set([''])
+    assert(combination(array) == result)
+    
+    array = ['a']
+    result = set(['a'])
+    assert(combination(array) == result)