offer37:两个链表的第一个公共节点

/** * Created by WHZ on 2017/4/7. */public class offer37 {    private class ListNode{        ListNode next;        int val;    }    ListNode FindFirstCommonNode(ListNode p1,ListNode p2){        int length1 = GetListLength(p1);        int length2 = GetListLength(p2);        int lengthDif = length1-length2;        ListNode pAhead = p1;        ListNode pBehind = p2;        if(length1<length2){            lengthDif = length2-length1;            pAhead = p2;            pBehind = p1;        }        for(int i=0;i<lengthDif;i++){            pAhead = pAhead.next;        }        while(pAhead!=null&&pBehind!=null&&pAhead!=pBehind){            pAhead = pAhead.next;            pBehind = pBehind.next;        }        return pAhead;    }    int GetListLength(ListNode head){        int length = 0;        ListNode node = head;        while(node!=null){            length++;            node = node.next;        }        return length;    }}