Create reverse_string.py

learning-zone · learning-zone · commit efe973cec3a3 · 2019-09-14T23:17:05.000+05:30
diff --git a/reverse_string.py b/reverse_string.py
@@ -0,0 +1,72 @@
+# Given a string, return the same string, reversed.
+# can't use .reverse()
+
+def rev_str(string):
+    """
+    >>> rev_str('hello')
+    'olleh'
+
+    >>> rev_str('1234h')
+    'h4321'
+
+    >>> rev_str('')
+    ''
+    """
+
+    # Runtime: O(n)
+
+    reversed_str = ""
+    list_str = list(string)
+    # ['h', 'e', l, l, o]
+    for l in range(len(list_str)):
+        letter = list_str.pop()
+        # l
+        reversed_str += letter
+        # oll
+    return reversed_str
+
+
+def rev_str_2(string):
+    """
+    >>> rev_str_2('hello')
+    'olleh'
+
+    >>> rev_str_2('1234h')
+    'h4321'
+
+    >>> rev_str_2('')
+    ''
+    """
+
+    # Runtime: O(n)
+
+    return string[::-1]
+
+
+def rev_str_3(string):
+    """
+    >>> rev_str_3('hello')
+    'olleh'
+
+    >>> rev_str_3('1234h')
+    'h4321'
+
+    >>> rev_str_3('')
+    ''
+    """
+
+    # Runtime: O(n)
+
+    if len(string) == 0:
+        return string
+
+    return string[-1] + rev_str_3(string[:-1])
+
+
+
+if __name__ == '__main__':
+    import doctest
+    results = doctest.testmod()
+
+    if results.failed == 0:
+        print "ALL TESTS PASSED!"
