Update palindrome.py (#1509)

* Update palindrome.py

Add Doctests.

* Use test_data to drive the testing

Author: percy07

other/palindrome.py

@@ -1,31 +1,66 @@
-# Program to find whether given string is palindrome or not
-def is_palindrome(str):
+# Algorithms to determine if a string is palindrome
+
+test_data = {
+    "MALAYALAM": True,
+    "String": False,
+    "rotor": True,
+    "level": True,
+    "A": True,
+    "BB": True,
+    "ABC": False,
+    "amanaplanacanalpanama": True,  # "a man a plan a canal panama"
+}
+# Ensure our test data is valid
+assert all((key == key[::-1]) is value for key, value in test_data.items())
+
+
+def is_palindrome(s: str) -> bool:
+    """
+    Return True if s is a palindrome otherwise return False.
+
+    >>> all(is_palindrome(key) is value for key, value in test_data.items())
+    True
+    """
+
     start_i = 0
-    end_i = len(str) - 1
+    end_i = len(s) - 1
     while start_i < end_i:
-        if str[start_i] == str[end_i]:
+        if s[start_i] == s[end_i]:
             start_i += 1
             end_i -= 1
         else:
             return False
     return True
 
 
-# Recursive method
-def recursive_palindrome(str):
-    if len(str) <= 1:
+def is_palindrome_recursive(s: str) -> bool:
+    """
+    Return True if s is a palindrome otherwise return False.
+
+    >>> all(is_palindrome_recursive(key) is value for key, value in test_data.items())
+    True
+    """
+    if len(s) <= 1:
         return True
-    if str[0] == str[len(str) - 1]:
-        return recursive_palindrome(str[1:-1])
+    if s[0] == s[len(s) - 1]:
+        return is_palindrome_recursive(s[1:-1])
     else:
         return False
 
 
-def main():
-    str = "ama"
-    print(recursive_palindrome(str.lower()))
-    print(is_palindrome(str.lower()))
+def is_palindrome_slice(s: str) -> bool:
+    """
+    Return True if s is a palindrome otherwise return False.
+
+    >>> all(is_palindrome_slice(key) is value for key, value in test_data.items())
+    True
+    """
+    return s == s[::-1]
 
 
 if __name__ == "__main__":
-    main()
+    for key, value in test_data.items():
+        assert is_palindrome(key) is is_palindrome_recursive(key)
+        assert is_palindrome(key) is is_palindrome_slice(key)
+        print(f"{key:21} {value}")
+    print("a man a plan a canal panama")