用快慢指针实现查找链表的中间值

ゝ一世哀愁。 2024-04-18 17:04 29阅读 0赞

快慢指针就是类似于合并排序过程中的步长那样一个指针每次走二一个走以等走到一半时第一个刚完基于此提高效率

package com.linkedlist;
    
    
    /**
     * @Auther: 大哥的叔
     * @Date: 2019/9/9 18:19
     * @Description:
     */
    public class ModList {
        static ListNode head = new ListNode(1);
    
        public static void main (String[] args) {
    
            ModList modList = new ModList();
            for (int i = 0; i < 10; i++) {
                modList.add(i + 1);
            }
            System.out.println();
            modList.display();
            modList.modNode(head);
            System.out.println();
    
        }
    
        public void add (int i) {
            ListNode temp = head;
            while (true) {
                if (temp.next == null) {
                    break;
                }
    
                temp = temp.next;
            }
            ListNode node = new ListNode(i);
            temp.next = node;
        }
    
        public void display () { //输出单链表中所有结点  
            ListNode p = head.next;
            while (p != null) {
                System.out.print(p.val + " ");
                p = p.next;
            }
            System.out.println();
        }
    
        public int length () {//求带头结点单链表的长度  
            int length = 0;
            ListNode p = head.next;
            while (p != null) {
                p = p.next;
                length++;
            }
            return length;
        }
    
    
        public ListNode modNode (ListNode modList) {
            if (head == null) {
                return null;
            }
            ListNode fast = head;
            ListNode slow = head;
            while (fast != null && fast.getNext() != null) {
                fast = fast.next.next;
                slow = slow.next;
            }
            if (length()% 2 == 0) System.out.println(slow.next.getVal());
            else System.out.println(slow.getVal());
            return slow;
    
        }
    }
    
    class ListNode {
        public int getVal () {
            return val;
        }
    
        public void setVal (int val) {
            this.val = val;
        }
    
        public ListNode getNext () {
            return next;
        }
    
        public void setNext (ListNode next) {
            this.next = next;
        }
    
        public int val;
        public ListNode next;
    
        public ListNode (int val) {
            this.val = val;
        }
    }