Create recursive_index.py

Author: learning-zone

recursive_index.py

@@ -0,0 +1,102 @@
+def recursive_index(needle, haystack):
+    """Given list (haystack), return index (0-based) of needle in the list.
+
+    Return None if needle is not in haystack.
+
+    Do this with recursion. You MAY NOT USE A `for` OR `while` LOOP.
+
+    >>> lst = ["hey", "there", "you"]
+
+    >>> recursive_index("hey", lst)
+    0
+
+    >>> recursive_index("you", lst)
+    2
+
+    >>> recursive_index("porcupine", lst) is None
+    True
+    """
+
+    if not haystack or needle not in haystack:
+        return None
+
+    count = 0
+
+    if needle == haystack[0]:
+        return count
+
+
+    count += 1 + recursive_index(needle, haystack[1:])
+
+    return count
+
+
+def recursive_index_2(needle, haystack):
+    """Given list (haystack), return index (0-based) of needle in the list.
+
+    Return None if needle is not in haystack.
+
+    Do this with recursion. You MAY NOT USE A `for` OR `while` LOOP.
+
+    >>> lst = ["hey", "there", "you"]
+
+    >>> recursive_index_2("hey", lst)
+    0
+
+    >>> recursive_index_2("you", lst)
+    2
+
+    >>> recursive_index_2("porcupine", lst) is None
+    True
+    """
+
+    if not haystack or needle not in haystack:
+        return None
+
+    if needle == haystack[0]:
+        return 0
+
+
+    else:
+        return 1 + recursive_index_2(needle, haystack[1:])
+
+
+def recursive_index_3(needle, haystack):
+    """Given list (haystack), return index (0-based) of needle in the list.
+
+    Return None if needle is not in haystack.
+
+    Do this with recursion. You MAY NOT USE A `for` OR `while` LOOP.
+
+    >>> lst = ["hey", "there", "you"]
+
+    >>> recursive_index_3("hey", lst)
+    0
+
+    >>> recursive_index_3("you", lst)
+    2
+
+    >>> recursive_index_3("porcupine", lst) is None
+    True
+    """
+
+    def _recursive_index_3(needle, haystack, count):
+
+        if len(haystack) == count:
+            return None
+
+        if needle == haystack[count]:
+            return count
+
+        return _recursive_index_3(needle, haystack, count+1)
+
+    return _recursive_index_3(needle, haystack, 0)
+
+
+
+if __name__ == '__main__':
+    import doctest
+    results = doctest.testmod()
+
+    if results.failed == 0:
+        print "ALL TESTS PASSED!"