不带头节点的链表有哪些缺点_23张图！万字详解「链表」，从小白到大佬！

private static class Node<E> {E item;Node<E> next;Node(E element, Node<E> next) {this.item = element;this.next = next;}
}

private static class Node<E> {E item;Node<E> next;Node<E> prev;Node(Node<E> prev, E element, Node<E> next) {this.item = element;this.next = next;this.prev = prev;}
}

package java.util;import java.util.function.Consumer;public class LinkedList<E>extends AbstractSequentialList<E>implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{// 链表大小transient int size = 0;// 链表头部transient Node<E> first;// 链表尾部transient Node<E> last;public LinkedList() {}public LinkedList(Collection<? extends E> c) {this();addAll(c);}// 获取头部元素public E getFirst() {final Node<E> f = first;if (f == null)throw new NoSuchElementException();return f.item;}// 获取尾部元素public E getLast() {final Node<E> l = last;if (l == null)throw new NoSuchElementException();return l.item;}// 删除头部元素public E removeFirst() {final Node<E> f = first;if (f == null)throw new NoSuchElementException();return unlinkFirst(f);}// 删除尾部元素public E removeLast() {final Node<E> l = last;if (l == null)throw new NoSuchElementException();return unlinkLast(l);}// 添加头部元素public void addFirst(E e) {linkFirst(e);}// 添加头部元素的具体执行方法private void linkFirst(E e) {final Node<E> f = first;final Node<E> newNode = new Node<>(null, e, f);first = newNode;if (f == null)last = newNode;elsef.prev = newNode;size++;modCount++;}// 添加尾部元素public void addLast(E e) {linkLast(e);}// 添加尾部元素的具体方法void linkLast(E e) {final Node<E> l = last;final Node<E> newNode = new Node<>(l, e, null);last = newNode;if (l == null)first = newNode;elsel.next = newNode;size++;modCount++;}// 查询链表个数public int size() {return size;}// 清空链表public void clear() {for (Node<E> x = first; x != null; ) {Node<E> next = x.next;x.item = null;x.next = null;x.prev = null;x = next;}first = last = null;size = 0;modCount++;}// 根据下标获取元素public E get(int index) {checkElementIndex(index);return node(index).item;}private static class Node<E> {E item;Node<E> next;Node<E> prev;Node(Node<E> prev, E element, Node<E> next) {this.item = element;this.next = next;this.prev = prev;}}// 忽略其他方法......
}

public class LinkedListTest {public static void main(String[] a) {LinkedList list = new LinkedList();list.add("Java");list.add("中文");list.add("社群");list.addFirst("头部添加"); // 添加元素到头部list.addLast("尾部添加");  // 添加元素到最后System.out.println(list);}
}

import java.util.LinkedList;public class LinkedListTest {public static void main(String[] a) {LinkedList list = new LinkedList();list.offer("头部");list.offer("中间");list.offer("尾部");list.removeFirst(); // 删除头部元素list.removeLast();  // 删除尾部元素System.out.println(list);}
}

import java.util.LinkedList;public class LinkedListTest {public static void main(String[] a) {LinkedList list = new LinkedList();list.offer("Java");list.offer("MySQL");list.offer("DB");// 修改list.set(2, "Oracle");System.out.println(list);}
}

import java.util.LinkedList;public class LinkedListTest {public static void main(String[] a) {LinkedList list = new LinkedList();list.offer("Java");list.offer("MySQL");list.offer("DB");// --- getXXX() 获取 ---// 获取最后一个System.out.println(list.getLast());// 获取首个System.out.println(list.getFirst());// 根据下标获取System.out.println(list.get(1));// peekXXX() 获取System.out.println("--- peek() ---");// 获取最后一个System.out.println(list.peekLast());// 获取首个System.out.println(list.peekFirst());// 根据首个System.out.println(list.peek());}
}

for (int size = linkedList.size(), i = 0; i < size; i++) {System.out.println(linkedList.get(i));
}

for (String str: linkedList) {System.out.println(str);
}

Iterator iter = linkedList.iterator();
while (iter.hasNext()) {System.out.println(iter.next());
}

LinkedList list = new LinkedList();
// 元素入列
list.add("Java");
list.add("中文");
list.add("社群");while (!list.isEmpty()) {// 打印并移除队头元素System.out.println(list.poll());
}

LinkedList list = new LinkedList();
// 元素入栈
list.add("Java");
list.add("中文");
list.add("社群");while (!list.isEmpty()) {// 打印并移除栈顶元素System.out.println(list.pollLast());
}

public ListNode reverseList(ListNode head) {if (head == null) return null;Stack<ListNode> stack = new Stack<>();stack.push(head); // 存入第一个节点while (head.next != null) {stack.push(head.next); // 存入其他节点head = head.next; // 指针移动的下一位}// 反转链表ListNode listNode = stack.pop(); // 反转第一个元素ListNode lastNode = listNode; // 临时节点，在下面的 while 中记录上一个节点while (!stack.isEmpty()) {ListNode item = stack.pop(); // 当前节点lastNode.next = item;lastNode = item;}lastNode.next = null; // 最后一个节点赋为null（不然会造成死循环）return listNode;
}

public static ListNode reverseList(ListNode head) {if (head == null || head.next == null) return head;// 从下一个节点开始递归ListNode reverse = reverseList(head.next);head.next.next = head; // 设置下一个节点的 next 为当前节点head.next = null; // 把当前节点的 next 赋值为 null，避免循环引用return reverse;
}

class Solution {public ListNode reverseList(ListNode head) {if (head == null) return null;// 最终排序的倒序链表ListNode prev = null;while (head != null) {// 循环的下个节点ListNode next = head.next;// 反转节点操作head.next = prev;// 存储下个节点的上个节点prev = head;// 移动指针到下一个循环head = next;}return prev;}
}