前 言 🍉 作者简介:半旧518,长跑型选手,立志坚持写10年博客,专注于java后端 ☕专栏简介:代码随想录leetcode速通训练营java版本 🌰 文章简介:leetcode-T203移除链表元素,leetcode-T707 设计链表,leetcode-T206 反转链表
解法: 还挺简单的,为了对第一个数据归一化操作,定义头指针,不含数据的虚拟头节点。
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
public ListNode removeElements(ListNode head, int val) {
if(head == null) {
return head;
}
ListNode p = new ListNode(-1, head);
ListNode pre = p;
ListNode cur = head;
while(cur != null) {
if(cur.val == val) {
pre.next = cur.next;
} else {
pre = cur;
}
cur = cur.next;
}
return p.next;
}
}
class ListNode {
int val;
ListNode next;
ListNode() {
}
ListNode(int val) {
this.val = val;
}
}
class MyLinkedList {
int size; //链表的大小
ListNode head; // 虚拟头节点
public MyLinkedList() {
size = 0;
head = new ListNode(-1);
}
public int get(int index) {
if(index > size - 1 || index < 0) {
return -1;
}
ListNode cur = head;
while(index-- >= 0) { // 包含虚拟头结点,所以查找索引为index + 1 的结点
cur = cur.next;
}
return cur.val;
}
public void addAtHead(int val) {
// addAtIndex(0, val);
ListNode temp = new ListNode(val);
temp.next = head.next;
head.next = temp;
size++;
}
public void addAtTail(int val) {
int index = size - 1;
ListNode cur = head;
while(index-- >= 0) {
cur = cur.next;
}
ListNode temp = new ListNode(val);
cur.next = temp;
size++;
}
public void addAtIndex(int index, int val) {
if(index > size) {
return;
}
size++;
if(index == size) {
addAtTail(val);
return;
}
if(index < 0) {
// index = 0;
addAtHead(val);
return;
}
ListNode cur = head;
while(index-- > 0) { // 找到前一个结点
cur = cur.next;
}
ListNode temp = new ListNode(val);
temp.next = cur.next;
cur.next = temp;
}
public void deleteAtIndex(int index) {
if(index < 0 || index > size - 1) {
return;
}
size--;
ListNode cur = head;
while(index-- > 0) { // 找到前一个结点
cur = cur.next;
}
cur.next = cur.next.next;
}
}
/**
* 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);
*/
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
public ListNode reverseList(ListNode head) {
ListNode prev = head;
if(head == null) {
return head;
}
ListNode cur = head.next;
while(cur != null) {
ListNode temp = cur.next;
cur.next = prev;
prev = cur;
cur = temp;
}
head.next = null;
return prev;
}
}