剑指offer编程试题Java实现--36.两个链表的第一个公共结点

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36.两个链表的第一个公共结点

题目描述
输入两个链表，找出它们的第一个公共结点。

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 lp1 = pHead1;
        ListNode lp2 = pHead2;
        ListNode pHeadLong = pHead1;
        ListNode pHeadShort = pHead2;
        int nLengthDif = 0;
        while(lp1 != null){
            len1++;
            lp1 = lp1.next;
        }
        while(lp2 != null){
            len2++;
            lp2 = lp2.next;
        }
        if(len2 > len1){
            pHeadLong = pHead2;
            pHeadShort = pHead1;
            nLengthDif = len2 - len1;
        }else{
            nLengthDif = len1 - len2;
        }

        for(int i = 0; i < nLengthDif; ++i)
            pHeadLong = pHeadLong.next;

        while(pHeadLong != null && pHeadShort != null && pHeadLong != pHeadShort){
            pHeadLong = pHeadLong.next;
            pHeadShort = pHeadShort.next;
        }
        ListNode res = pHeadLong;
        return res;
    }
}