707. Design Linked List

Posted on 4 mins read

1. Description

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 $index^{th}$ 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 $index^{th}$ 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 $index^{th}$ node in the linked list, if the index is valid.

2. Example

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

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.

4. Solutions

My Accepted Solution(Follow Up)

n is the number of nodes in the list
Time complexity(MyListNode): O(1)
Time complexity(get): O(n)
Time complexity(addAtHead): O(1)
Time complexity(addAtTail): O(1)
Time complexity(addAtIndex): O(n)
Time complexity(deleteAtIndex): O(n)
Space complexity: O(n)

class MyListNode {
public:
    MyListNode* prev;
    MyListNode* next;
    int val;

    MyListNode(int value = -1) : prev(nullptr), next(nullptr), val(value) {}
};

class MyLinkedList {
public:
    /** Initialize your data structure here. */
    MyLinkedList() {
        guardHead = new MyListNode();
        guardHead->next = guardHead;
        guardHead->prev = guardHead;

        size = 0;
    }

    /** Get the value of the index-th node in the linked list. If the index is invalid, return -1.
     */
    int get(int index) {
        if (index < 0 || index >= size) {
            return -1;
        }

        bool frontToBack = (index < size / 2);
        auto iter = (frontToBack ? guardHead->next : guardHead->prev);
        for (int i = 0; i < (frontToBack ? index : size - index - 1); ++i) {
            iter = (frontToBack ? iter->next : iter->prev);
        }
        return iter->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 addAtHead(int val) {
        insertNode(guardHead, guardHead->next, val);

        ++size;
    }

    /** Append a node of value val to the last element of the linked list. */
    void addAtTail(int val) {
        insertNode(guardHead->prev, guardHead, val);

        ++size;
    }

    /** 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. */
    void addAtIndex(int index, int val) {
        if (0 <= index && index < size) {
            auto iter = guardHead->next;
            for (int i = 0; i < index; ++i) {
                iter = iter->next;
            }

            insertNode(iter->prev, iter, val);
            ++size;
        } else if (index == size) {
            insertNode(guardHead->prev, guardHead, val);
            ++size;
        } else {
            // do nothing
        }
    }

    /** Delete the index-th node in the linked list, if the index is valid. */
    void deleteAtIndex(int index) {
        if (0 <= index && index < size) {
            auto iter = guardHead->next;
            for (int i = 0; i < index; ++i) {
                iter = iter->next;
            }

            deleteNode(iter);

            --size;
        }
    }

private:
    int size;
    MyListNode* guardHead;

    void insertNode(MyListNode* prevNode, MyListNode* nextNode, int value) {
        auto nodeToInsert = new MyListNode(value);

        nodeToInsert->prev = prevNode;
        nodeToInsert->next = nextNode;
        prevNode->next = nodeToInsert;
        nextNode->prev = nodeToInsert;
    }

    void deleteNode(MyListNode* nodeToDelete) {
        nodeToDelete->prev->next = nodeToDelete->next;
        nodeToDelete->next->prev = nodeToDelete->prev;
    }
};
comments powered by Disqus