some changes

Array problems/Dequeue/deque.py

@@ -0,0 +1,108 @@
+class Node:
+    def __init__(self, value):
+        self.value = value
+        self.next = None
+        self.prev = None
+
+
+class Deque:
+    def __init__(self):
+        self.head = None
+        self.tail = None
+        self.size = 0
+
+    def is_empty(self):
+        return self.size == 0
+
+    def append(self, value):
+        new_node = Node(value)
+        if self.tail is None:  # Deque is empty
+            self.head = self.tail = new_node
+        else:
+            self.tail.next = new_node
+            new_node.prev = self.tail
+            self.tail = new_node
+        self.size += 1
+
+    def appendleft(self, value):
+        new_node = Node(value)
+        if self.head is None:  # Deque is empty
+            self.head = self.tail = new_node
+        else:
+            new_node.next = self.head
+            self.head.prev = new_node
+            self.head = new_node
+        self.size += 1
+
+    def pop(self):
+        if self.is_empty():
+            raise IndexError("pop from an empty deque")
+
+        value = self.tail.value
+        if self.head == self.tail:  # Only one element in the deque
+            self.head = self.tail = None
+        else:
+            self.tail = self.tail.prev
+            self.tail.next = None
+
+        self.size -= 1
+        return value
+
+    def popleft(self):
+        if self.is_empty():
+            raise IndexError("pop from an empty deque")
+
+        value = self.head.value
+        if self.head == self.tail:  # Only one element in the deque
+            self.head = self.tail = None
+        else:
+            self.head = self.head.next
+            self.head.prev = None
+
+        self.size -= 1
+        return value
+
+    def peek(self):
+        if self.is_empty():
+            return None
+        return self.tail.value
+
+    def peekleft(self):
+        if self.is_empty():
+            return None
+        return self.head.value
+
+    def __len__(self):
+        return self.size
+
+    def __str__(self):
+        elements = []
+        current = self.head
+        while current:
+            elements.append(current.value)
+            current = current.next
+        return "Deque: " + " <-> ".join(map(str, elements))
+
+
+# Example usage
+if __name__ == "__main__":
+    deque = Deque()
+
+    deque.append(10)
+    deque.append(20)
+    deque.appendleft(5)
+    deque.appendleft(1)
+
+    print(deque)  # Deque: 1 <-> 5 <-> 10 <-> 20
+
+    print(deque.pop())  # 20
+    print(deque.popleft())  # 1
+
+    print(deque)  # Deque: 5 <-> 10
+
+    deque.append(30)
+    deque.appendleft(2)
+
+    print(deque)  # Deque: 2 <-> 5 <-> 10 <-> 30
+    print("Peek:", deque.peek())  # Peek: 30
+    print("Peek Left:", deque.peekleft())  # Peek Left: 2