剑指offer 题解 | #两个链表的第一个公共结点#

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) {
        // 求公共节点，不是相同的数字，所以可以直接用相同指针来判断。
        ListNode p = pHead1;
        ListNode q = pHead2;
        int count1 = 0;
        int count2 = 0;
        while(p!=null){
            count1++;
            p = p.next;
        }
        while(q!=null){
            count2++;
            q = q.next;
        }
        // 计算出差值，将长的移动到相应位置
        int count = Math.abs(count1 - count2);
        if(count1 < count2){
            p = pHead2;
            q = pHead1;
        }else{
            p = pHead1;
            q = pHead2;
        }
        while(p!=null && count>0){
            p = p.next;
            count--;
        }
        // 遍历
        while(p!=null && q!=null){
            if(p == q){
                return p;
            }
            p = p.next;
            q = q.next;
        }
        return null;
    }
}