输入两个链表，找出它们的第一个公共结点

Posted 2022-01-05 a1225234

import java.util.*;
/*
public class ListNode 
    int val;
    ListNode next = null;

    ListNode(int val) 
        this.val = val;
    
*/
public class Solution 
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) 
        ListNode head = pHead1;
        Set<ListNode> res= new HashSet<ListNode>();
        while(head!=null)
            res.add(head);
            head = head.next;
        
        head = pHead2;
        while(head!=null)
            if(res.contains(head))
                break;
            head = head.next;
        
        return head;
    

求出两个链表长度差

import java.util.*;
/*
public class ListNode 
    int val;
    ListNode next = null;

    ListNode(int val) 
        this.val = val;
    
*/
public class Solution 
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) 
        int len1=0,len2=0;
        ListNode head = pHead1;
        while(head!=null)
            len1++;
            head = head.next;
        
        head = pHead2;
        while(head!=null)
            len2++;
            head = head.next;
        
        ListNode maxList=null,minList=null;
        int lenc = Math.abs(len1-len2);
        if(len1>=len2)
            maxList = pHead1;
            minList = pHead2;
        
        if(len2>len1)
            maxList = pHead2;
            minList = pHead1;
        
        while(lenc!=0)
            maxList = maxList.next;
            lenc--;
        
        while(maxList!=minList)
            maxList = maxList.next;
            minList = minList.next;
        
        return maxList;