Create design-linked-list.py

Author: kamyu104

Python/design-linked-list.py

@@ -0,0 +1,107 @@
+# Time:  O(n)
+# Space: O(n)
+
+class Node:
+    def __init__(self, value):
+        self.val = value
+        self.next = self.prev = None
+
+
+class MyLinkedList(object):
+
+    def __init__(self):
+        """
+        Initialize your data structure here.
+        """
+        self.__head = self.__tail = Node(-1)
+        self.__head.next = self.__tail
+        self.__tail.prev = self.__head
+        self.__size = 0
+
+    def get(self, index):
+        """
+        Get the value of the index-th node in the linked list. If the index is invalid, return -1.
+        :type index: int
+        :rtype: int
+        """
+        if 0 <= index <= self.__size // 2:
+            return self.__forward(0, index, self.__head.next).val
+        elif self.__size // 2 < index < self.__size:
+            return self.__backward(self.__size, index, self.__tail).val
+        return -1
+
+    def addAtHead(self, val):
+        """
+        Add a node of value val before the first element of the linked list.
+        After the insertion, the new node will be the first node of the linked list.
+        :type val: int
+        :rtype: void
+        """
+        self.__add(self.__head, val)
+
+    def addAtTail(self, val):
+        """
+        Append a node of value val to the last element of the linked list.
+        :type val: int
+        :rtype: void
+        """
+        self.__add(self.__tail.prev, val)
+
+    def addAtIndex(self, index, val):
+        """
+        Add a node of value val before the index-th node in the linked list.
+        If index equals to the length of linked list,
+        the node will be appended to the end of linked list.
+        If index is greater than the length, the node will not be inserted.
+        :type index: int
+        :type val: int
+        :rtype: void
+        """
+        if 0 <= index <= self.__size // 2:
+            self.__add(self.__forward(0, index, self.__head.next).prev, val)
+        elif self.__size // 2 < index <= self.__size:
+            self.__add(self.__backward(self.__size, index, self.__tail).prev, val)
+
+    def deleteAtIndex(self, index):
+        """
+        Delete the index-th node in the linked list, if the index is valid.
+        :type index: int
+        :rtype: void
+        """
+        if 0 <= index <= self.__size // 2:
+            self.__remove(self.__forward(0, index, self.__head.next))
+        elif self.__size // 2 < index < self.__size:
+            self.__remove(self.__backward(self.__size, index, self.__tail))
+
+    def __add(self, preNode, val):
+        node = Node(val)
+        node.prev = preNode
+        node.next = preNode.next
+        node.prev.next = node.next.prev = node
+        self.__size += 1
+        
+    def __remove(self, node):
+        node.prev.next = node.next
+        node.next.prev = node.prev
+        self.__size -= 1
+        
+    def __forward(self, start, end, curr):
+        while start != end:
+            start += 1
+            curr = curr.next
+        return curr
+    
+    def __backward(self, start, end, curr):
+        while start != end:
+            start -= 1
+            curr = curr.prev
+        return curr
+
+
+# Your MyLinkedList object will be instantiated and called as such:
+# obj = MyLinkedList()
+# param_1 = obj.get(index)
+# obj.addAtHead(val)
+# obj.addAtTail(val)
+# obj.addAtIndex(index,val)
+# obj.deleteAtIndex(index)