Palindrome using deque (#803)

* Add method using deque

* updated tests for is_palindrome.py deque

Author: bhanu-pappala

algorithms/strings/is_palindrome.py

@@ -11,6 +11,7 @@
 we define empty string as valid palindrome.
 """
 from string import ascii_letters
+from collections import deque
 
 
 def is_palindrome(s):
@@ -85,3 +86,20 @@ def is_palindrome_stack(s):
         if s[i] != stack.pop():
             return False
     return True	
+
+# Variation 4 (using deque)
+def is_palindrome_deque(s):
+    s = remove_punctuation(s)
+    deq = deque()
+    for char in s:
+        deq.appendleft(char)
+
+    equal = True
+
+    while len(deq) > 1 and equal:
+        first = deq.pop()
+        last = deq.popleft()
+        if first != last :
+            equal = False
+
+    return equal

tests/test_strings.py

@@ -8,7 +8,7 @@
     group_anagrams,
     int_to_roman,
     is_palindrome, is_palindrome_reverse,
-    is_palindrome_two_pointer, is_palindrome_stack,
+    is_palindrome_two_pointer, is_palindrome_stack, is_palindrome_deque, 
     is_rotated, is_rotated_v1,
     license_number,
     make_sentence,
@@ -195,6 +195,11 @@ def test_is_palindrome_stack(self):
         self.assertTrue(is_palindrome_stack("Otto"))
         self.assertFalse(is_palindrome_stack("house"))
 
+    def test_is_palindrome_deque(self):
+        # 'Otto' is a old german name.
+        self.assertTrue(is_palindrome_deque("Otto"))
+        self.assertFalse(is_palindrome_deque("house"))
+
 
 class TestIsRotated(unittest.TestCase):
     """[summary]