Leetcode: Design Linked List

Posted on July 19, 2018September 23, 2019 by braindenny

Design Linked List

Similar Problems:

Design your implementation of the linked list. You can choose to use the singly linked list or the 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 these functions in your linked list class:

get(index) : Get the value of the index-th node in the linked list. If the index is invalid, return -1.
addAtHead(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.
addAtTail(val) : Append a node of value val to the last element of the linked list.
addAtIndex(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.
deleteAtIndex(index) : Delete the index-th node in the linked list, if the index is valid.

Example:

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

Note:

All values will be in the range of [1, 1000].
The number of operations will be in the range of [1, 1000].
Please do not use the built-in LinkedList library.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

Solution:

// https://code.dennyzhang.com/design-linked-list
// Basic Ideas:
// head pointer won't store data
//
// Complexity: Time O(1), Space O(1)
type LinkedNode struct {
    value int
    next *LinkedNode
}

type MyLinkedList struct {
    head *LinkedNode
    tail *LinkedNode
}

/** Initialize your data structure here. */
func Constructor() MyLinkedList {
    p := LinkedNode{0, nil}
    return MyLinkedList{&p, &p}
}


/** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
func (this *MyLinkedList) Get(index int) int {
    if index<0 { return -1 }
    p := this.head.next
    for index>0 && p != nil { index, p = index-1, p.next }
    if p == nil { return -1 }
    return p.value
}


/** 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. */
func (this *MyLinkedList) AddAtHead(val int)  {
    p := LinkedNode{val, this.head.next}
    // add to the tail
    if this.head == this.tail { this.tail = &p }
    this.head.next = &p
}

/** Append a node of value val to the last element of the linked list. */
func (this *MyLinkedList) AddAtTail(val int)  {
    p := LinkedNode{val, nil}
    this.tail.next = &p
    this.tail = &p
}

/** 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. */
func (this *MyLinkedList) AddAtIndex(index int, val int)  {
    if index < 0 { return }
    p := this.head
    for index>0 && p != nil { index, p = index-1, p.next }
    if p == nil { return }
    q := LinkedNode{val, p.next}
    // add to the tail
    if p == this.tail { this.tail = &q }
    p.next = &q
}


/** Delete the index-th node in the linked list, if the index is valid. */
func (this *MyLinkedList) DeleteAtIndex(index int)  {
    if index < 0 { return }
    p := this.head
    for index>0 && p != nil { index, p = index-1, p.next }
    if p == nil || p.next == nil { return }
    // delete from the tail
    if p.next == this.tail { this.tail = p }
    p.next = p.next.next
}


/**
 * Your MyLinkedList object will be instantiated and called as such:
 * obj := Constructor();
 * param_1 := obj.Get(index);
 * obj.AddAtHead(val);
 * obj.AddAtTail(val);
 * obj.AddAtIndex(index,val);
 * obj.DeleteAtIndex(index);
 */

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