LeetCode 707. Design Linked List

[wupangyen]

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.

[wupangyen]

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

[wupangyen]

we try to implement a singly linked list create a node class first have val and next node

in constructer we have head node and we have size of singly linked list.

get func

check edge case if index >= size , which is invalid we return -1; loop through the linked list

until the current node is in the index we want to get. return the value of the node

addAtHead func we use the addAtIndex func (0,val)

addAttail func we use addAtIndex(size,val)

atAddIndex func if index is invalid return

move current node to 1 index before the index we want to add

create a new node add the val we want in it

new node . next = curr.next curr.next = new node increment size

deleteAtIndex func check invalid index

move current to the node we want to remove

curr.next = curr.next.next break the pointer

decrement size

[wupangyen]

class MyLinkedList {

/*
create node class
*/
public class Node{
    int val;
    Node next;
    public Node(int val){
        this.val = val;
    }
}
Node head;
// keep track of the size of the singly linked list
int size;

/** Initialize your data structure here. */
public MyLinkedList() {
    head = new Node(-1);
    size = 0;

}

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

    // we need a way to iterate through the linked list
    // 0 1 2
    Node curr = head;
    int count = 0;
    while(count <= index){
        curr = curr.next;
        count += 1;
    }

    return curr.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. */
public void addAtHead(int val) {
    addAtIndex(0,val);

}

/** Append a node of value val to the last element of the linked list. */
public void addAtTail(int val) {
    addAtIndex(size,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. */
public void addAtIndex(int index, int val) {
    if(index > size){
        return;
    }

    // add a node of value val before the index th node in the linked list.
    int count = 0;
    Node curr = head;
    while(count < index){
        curr = curr.next;
        count += 1;
    }

    Node toAdd = new Node(val);
    toAdd.next = curr.next;
    curr.next = toAdd;
    size ++;

}

/** Delete the index-th node in the linked list, if the index is valid. */
public void deleteAtIndex(int index) {
    if(index >= size){
        return;
    }

    int count = 0;
    Node curr = head;
    while(count < index){
        curr = curr.next;
        count += 1;
    }

    curr.next = curr.next.next;
    size--;

}

}

/**

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