【編程打卡】兩個鏈表的第一個公共節點（Java實現）

【編程打卡】兩個鏈表的第一個公共節點（Java實現）

題目來源

劍指offer第36題
https://www.nowcoder.com/practice/6ab1d9a29e88450685099d45c9e31e46?tpId=13&tqId=11189&tPage=2&rp=2&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking

題目描述

輸入兩個鏈表，找出它們的第一個公共結點。

題目代碼

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
import java.util.*;
public class Solution {
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
         Set<ListNode>set=new HashSet<>();
        while(pHead1!=null){
            set.add(pHead1);
            pHead1=pHead1.next;
        }
         while(pHead2!=null){
            if(set.contains(pHead2))
                return pHead2;
            pHead2=pHead2.next;
        }
        return pHead2;
    }
}

/*
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 d=null;
        int i=0;
        ListNode l1=pHead1;
        ListNode l2=pHead2;
        int count1=countlength(pHead1);
        int count2=countlength(pHead2);
        int x;
        if(count1<count2){
            x=count2-count1;
             while(x-->0){
                  pHead2=pHead2.next;
             }
        }else
        {
            x=count1-count2;
            while(x-->0){
                  pHead1=pHead1.next;
             }
        }
        while(pHead1!=null&&pHead2!=null){
             if(pHead1==pHead2)
                      return pHead1;
                  pHead1=pHead1.next;
                  pHead2=pHead2.next;
                  
              }
        return d;
    }
    int countlength(ListNode pHead1){
        int count1=0;
        while(pHead1!=null){
            pHead1=pHead1.next;
            count1++;
        }
        return count1;
    }
}