牛客（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 static class ListNode {
        int val;
        ListNode next = null;

        ListNode(int val) {
            this.val = val;
        }
    }

    public static ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
        if (pHead1 == null||pHead2 == null) {
            return null;
        }
        int count1=0;
        ListNode p1 = pHead1;
        while(p1!=null){
            count1++;
            p1 = p1.next;
        }
        int count2=0;
        ListNode p2 = pHead2;

        while(p2!=null){
            count2++;
            p2 = p2.next;
        }
        if (count1>count2){
            while (count1>count2){
                pHead1 = pHead1.next;
                count1--;
            }
        }
        if (count1<count2){
            while (count1<count2){
                pHead2 = pHead2.next;
                count2--;
            }
        }
        while (pHead1!=pHead2){
            pHead2 = pHead2.next;
            pHead1 = pHead1.next;
        }
        return pHead2;

    }