力扣题目链接

单链表

class ListNode {int val;ListNode next;public ListNode(int val) {this.val = val;}
}
class MyLinkedList {int size;ListNode head;public MyLinkedList() {size = 0;head = new ListNode(0);}public int get (int index) {if ( index < 0 || index >= size) return -1;ListNode temp = head;for (int i = 0; i <= index; i++) {temp = temp.next;}return temp.val;}public void addAtHead(int val) {addAtIndex(0,val);}public void addAtTail(int val) {addAtIndex(size,val);}public void addAtIndex(int index, int val) {if (index < 0 ||index > size) return;ListNode temp = head;for (int i = 0; i < index; i++) {temp = temp.next;}ListNode p = new ListNode(val);p.next = temp.next;temp.next = p;size ++;}public void deletAtIndex(int index) {if (index < 0 || index >= size) return;ListNode temp = head;for (int i = 0; i < index; i++) {temp = temp.next;}temp.next = temp.next.next;size --;}
}

双链表

class ListNode {int val;ListNode next;ListNode prev;public ListNode(int val) {this.val = val;}
}
class MyLinkedList {int size;ListNode head,tail;public MyLinkedList() {size = 0;head = new ListNode(0);tail = new ListNode(0);head.next = tail;tail.prev = head;}public int get(int index) {//判断index是否有效if (index < 0 || index >= size) return -1;ListNode temp = head;//判断哪边遍历时间最短if (index >= size / 2) {//从tail开始；temp = tail;for (int i = 0; i < size - index; i ++) {temp = temp.prev;}}else {//从head开始：for (int i = 0; i <= index; i++) {temp = temp.next;}}return temp.val;}public void addAtHead(int val) {addAtIndex(0,val);}public void addAtTail(int val) {addAtIndex(size,val);}public void addAtIndex(int index, int val) {if (index < 0 || index > size) return;ListNode temp = head;for (int i = 0; i < index; i ++) {temp = temp.next;}ListNode p = new ListNode(val);p.next = temp.next;temp.next.prev = p;temp.next = p;p.prev = temp;size ++;}public void deleteAtIndex(int index) {if (index < 0 || index >= size) return;ListNode temp = head;for (int i = 0; i <= index; i++) {temp = temp.next;}temp.prev.next = temp.next;temp.next.prev = temp.prev;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);*/