链表应用

链表实现栈

public class LinkedListStack<E> implements Stack<E> {

	private LinkList<E> list;
	public LinkedListStack() {
		list = new LinkList<>();
	}
	@Override
	public void push(E e) {
		list.addFirst(e);
	}

	@Override
	public E pop() {
		return list.removeFirst();
	}

	@Override
	public E peek() {
		return list.getFirst();
	}

	@Override
	public int getSize() {
		return list.getSize();
	}

	@Override
	public boolean isEmpty() {
		return list.isEmpty();
	}
	@Override
	public String toString() {
		StringBuilder res = new StringBuilder();
		res.append("Stack:top");
		res.append(list);
		return res.toString();
	}
}

链表实现队列

public class LinkedListQueue<E> implements Queue<E> {
	private class Node {
 		public E e;
    	public Node next;

		public Node(E e,Node next) {
			this.e = e;
			this.next = next;
		}

		public Node(E e) {
			this(e,null);
		}
		public Node() {
			this(null,null);
		}
		public String toString() {
			return e.toString();
		}
	}

	private Node head, tail;
	private int size;

	public LinkedListQueue() {
		head = null;
		tail = null;
		size = 0;
	}
	public int getSize() {
		return size;
	}
	public boolean isEmpty() {
		return size == 0;
	}
	public void enqueue(E e) {
		if(tail == null) {
			tail = new Node(e);
			head = tail;
		} else {
			tail.next = new Node(e);
			tail = tail.next;
		}
		size ++;
	}
	public void dequeue() {
		if(isEmpty()) {
			throw new IllegalArgumentException("Cannot dequeue from an empty queue");
		}
		Node reNode = head;
		head = head.next;
		retNode.next = null;
		if(head == null) {
			tail = null;
		}
		size --;
		return retNode.e;
	}
}

链表与递归

移除链表元素
删除链表中等于给定值 val 的所有节点。

示例:

输入: 1->2->6->3->4->5->6, val = 6
输出: 1->2->3->4->5

public class Solution {

	public ListNode removeElements(ListNode head, int val) {
    // 创建虚拟节点
		ListNode dummyHead = new ListNode(0);
		dummyHead.next = head;
    for(ListNode pre = dummyHead; pre.next != null;) {
      	if(pre.next.val == val) {
          pre.next = pre.next.next;
        } else {
          pre = pre.next;
        }
    }
	}
}

把递归过程想成一个子函数，在子函数中写处理逻辑来解决上层函数的问题。

public class Solution {

	public ListNode removeElements(ListNode head, int val) {
		if(head == null){
			return null;
		}
		head.next = removeElements(head.next,val);
		return head.val == val? head.next: head;
	}
}