LeetCode in Kotlin

707. Design Linked List

Medium

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.

Solution

class MyLinkedList {
    private class Node(var `val`: Int) {
        var next: Node? = null
    }

    private var head: Node?
    private var tail: Node? = null
    private var size: Int

    init {
        head = tail
        size = 0
    }

    operator fun get(index: Int): Int {
        if (index >= size) {
            return -1
        }
        if (index == 0) {
            return head!!.`val`
        }
        var i = 0
        var ptr = head
        while (i++ < index - 1) {
            ptr = ptr!!.next
        }
        return ptr!!.next!!.`val`
    }

    fun addAtHead(`val`: Int) {
        val node = Node(`val`)
        if (head == null) {
            tail = node
            head = tail
            size++
            return
        }
        node.next = head
        head = node
        size++
    }

    fun addAtTail(`val`: Int) {
        if (head == null) {
            addAtHead(`val`)
            return
        }
        val node = Node(`val`)
        tail!!.next = node
        tail = node
        size++
    }

    fun addAtIndex(index: Int, `val`: Int) {
        if (index > size) {
            return
        }
        if (index == 0) {
            addAtHead(`val`)
            return
        }
        if (index == size) {
            addAtTail(`val`)
            return
        }
        var i = 0
        val node = Node(`val`)
        var ptr = head
        while (i++ < index - 1) {
            ptr = ptr!!.next
        }
        node.next = ptr!!.next
        ptr.next = node
        size++
    }

    fun deleteAtIndex(index: Int) {
        if (index >= size) {
            return
        }
        if (index == 0) {
            head = head!!.next
            size--
            return
        }
        var i = 0
        var ptr = head
        while (i++ < index - 1) {
            ptr = ptr!!.next
        }
        ptr!!.next = ptr.next!!.next
        if (index == size - 1) {
            tail = ptr
        }
        size--
    }
}

/*
 * Your MyLinkedList object will be instantiated and called as such:
 * var obj = MyLinkedList()
 * var param_1 = obj.get(index)
 * obj.addAtHead(`val`)
 * obj.addAtTail(`val`)
 * obj.addAtIndex(index,`val`)
 * obj.deleteAtIndex(index)
 */

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