Algorithm

Problem Name: 707. Design Linked List

Problem Link: https://leetcode.com/problems/design-linked-list/


Design your implementation of the linked list. You can choose to use a singly or doubly linked list.
A node in a singly linked list should have two attributes: val and next. val is the value of the current node, and next is a pointer/reference to the next node.
If you want to use the doubly linked list, you will need one more attribute prev to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.

Implement the MyLinkedList class:

  • MyLinkedList() Initializes the MyLinkedList object.
  • int get(int index) Get the value of the indexth node in the linked list. If the index is invalid, return -1.
  • void addAtHead(int 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.
  • void addAtTail(int val) Append a node of value val as the last element of the linked list.
  • void addAtIndex(int index, int val) Add a node of value val before the indexth node in the linked list. If index equals the length of the linked list, the node will be appended to the end of the linked list. If index is greater than the length, the node will not be inserted.
  • void deleteAtIndex(int index) Delete the indexth node in the linked list, if the index is valid.

 

Example 1:

Input
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"]
[[], [1], [3], [1, 2], [1], [1], [1]]
Output
[null, null, null, null, 2, null, 3]

Explanation
MyLinkedList myLinkedList = new MyLinkedList();
myLinkedList.addAtHead(1);
myLinkedList.addAtTail(3);
myLinkedList.addAtIndex(1, 2);    // linked list becomes 1->2->3
myLinkedList.get(1);              // return 2
myLinkedList.deleteAtIndex(1);    // now the linked list is 1->3
myLinkedList.get(1);              // return 3

 

Constraints:

  • 0 <= index, val <= 1000
  • Please do not use the built-in LinkedList library.
  • At most 2000 calls will be made to get, addAtHead, addAtTail, addAtIndex and deleteAtIndex.
 

Code Examples

#1 Code Example with Javascript Programming

Code - Javascript Programming


var MyLinkedList = function() {
  this.arr = []
}

MyLinkedList.prototype.get = function(index) {
  if (this.arr[index] !== undefined) {
    return this.arr[index]
  } else {
    return -1
  }
}

MyLinkedList.prototype.addAtHead = function(val) {
  this.arr.unshift(val)
}

MyLinkedList.prototype.addAtTail = function(val) {
  this.arr.push(val)
}

MyLinkedList.prototype.addAtIndex = function(index, val) {
  if (this.arr.length >= index) {
    this.arr.splice(index, 0, val)
  }
  if (index < 0) {
    this.arr.unshift(val)
  }
}

MyLinkedList.prototype.deleteAtIndex = function(index) {
  if (index >= 0 && index < this.arr.length) {
    this.arr.splice(index, 1)
  }
}
Copy The Code & Try With Live Editor

Input

x
–
+
cmd
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"] [[], [1], [3], [1, 2], [1], [1], [1]]

Output

x
–
+
cmd
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"] [[], [1], [3], [1, 2], [1], [1], [1]]

#2 Code Example with Python Programming

Code - Python Programming


class Node:
    def __init__(self, value):
        self.val = value
        self.next = self.pre = None
class MyLinkedList:

    def __init__(self):
        self.head = self.tail = Node(-1)
        self.head.next = self.tail
        self.tail.pre = self.head
        self.size = 0
        
    def add(self, preNode, val):
        node = Node(val)
        node.pre = preNode
        node.next = preNode.next
        node.pre.next = node.next.pre = node
        self.size += 1
        
    def remove(self, node):
        node.pre.next = node.next
        node.next.pre = node.pre
        self.size -= 1
        
    def forward(self, start, end, cur):
        while start != end:
            start += 1
            cur = cur.next
        return cur
    
    def backward(self, start, end, cur):
        while start != end:
            start -= 1
            cur = cur.pre
        return cur
    
    def get(self, index):
        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 - 1, index, self.tail.pre).val
        return -1

    def addAtHead(self, val):
        self.add(self.head, val)

    def addAtTail(self, val):
        self.add(self.tail.pre, val)

    def addAtIndex(self, index, val):
        if 0 <= index <= self.size // 2:
            self.add(self.forward(0, index, self.head.next).pre, val)
        elif self.size // 2 < index <= self.size:
            self.add(self.backward(self.size, index, self.tail).pre, val)

    def deleteAtIndex(self, index):
        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 - 1, index, self.tail.pre))
Copy The Code & Try With Live Editor

Input

x
–
+
cmd
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"] [[], [1], [3], [1, 2], [1], [1], [1]]

Output

x
–
+
cmd
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"] [[], [1], [3], [1, 2], [1], [1], [1]]
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