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108 lines (91 loc) · 3.57 KB
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// 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.
// See: https://leetcode.com/problems/design-linked-list/
package leetcode.design;
public class DesignLinkedList {
class MyLinkedList {
class ListNode {
int val;
ListNode next;
ListNode(int val) {
this.val = val;
}
}
private ListNode nullHead;
public MyLinkedList() {
nullHead = new ListNode(-1);
}
/**
* Get the value of the index-th node in the linked list. If the index is
* invalid, return -1.
*/
public int get(int index) {
ListNode head = nullHead;
for (int i = 0; i < index; i++)
head = head.next;
if (head.next == null)
return -1;
return head.next.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) {
ListNode tmp = nullHead.next;
nullHead.next = new ListNode(val);
nullHead.next.next = tmp;
}
// TODO: The current time complexity for this operation is O(n).
// Implement this operation in O(1) time (for example you can keep the tail).
/** Append a node of value val to the last element of the linked list. */
public void addAtTail(int val) {
ListNode head = nullHead;
while (head != null && head.next != null)
head = head.next;
head.next = new ListNode(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) {
ListNode head = nullHead;
for (int i = 0; i < index; i++)
head = head.next;
ListNode tmp = head.next;
head.next = new ListNode(val);
head.next.next = tmp;
}
/** Delete the index-th node in the linked list, if the index is valid. */
public void deleteAtIndex(int index) {
ListNode head = nullHead;
for (int i = 0; i < index; i++)
if (head.next != null)
head = head.next;
if (head != null && head.next != null)
head.next = head.next.next;
}
// public void print() {
// String res = "";
// ListNode head = nullHead.next;
// while (head != null) {
// res += head.val;
// res += "->";
// head = head.next;
// }
// System.out.println(res);
// }
}
public static void main(String[] args) {
MyLinkedList l = new DesignLinkedList().new MyLinkedList();
l.addAtHead(1);
l.addAtTail(3);
l.addAtIndex(1, 2);
}
}