MyQueue

package MyQueue;

import org.w3c.dom.ls.LSInput;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: czt20
 * Date: 2025 -12-18
 * Time: 21:53
 */
public class MyQueue {
    static class ListNode{
        public int val;
        public ListNode pre;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }
    public ListNode first=null;
    public ListNode last=null;
    public int usedsize=0;
    ListNode cur=first;
    public void offer(int val){
        ListNode node=new ListNode(val);
        if (isEmpty()){
            first=last=node;//first和last连接就靠这里！！！！！！！！！！
        }
        last.next=node;
        node.pre=last;
        last=node;
        usedsize++;
    }
    public int poll(){
        if (first==null){
            return -1;
        }
        ListNode curN=first;
        first=first.next;
        if(first!=null){
            first.pre=null;
        }
        usedsize--;
        return curN.val;
    }
    public int size(){
        return usedsize;
    }
    public int peek(){
        return first.val;
    }
    public boolean isEmpty(){
        if (first==null){
            return true;
        }
        return false;
    }
}