剑指offer 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。

/**
     * 遍历两个链表得到它们的长度
     * 第二次遍历,在较长的链表上先走若干步,接着同时在两个链表上遍历
     * @param pHead1
     * @param pHead2
     * @return
     */
    public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
        int len1 = getListLength(pHead1);
        int len2 = getListLength(pHead2);
        int len = len1 - len2;
        ListNode pHeadLong = pHead1;
        ListNode pHeadShort = pHead2;
        if (len2 > len1) {
            pHeadLong = pHead2;
            pHeadShort = pHead1;
            len = len2 - len1;
        }
        for (int i = 0; i < len; i++) {
            pHeadLong = pHeadLong.next;
        }
        while (pHeadLong != null && pHeadShort != null) {
            if (pHeadLong == pHeadShort) {
                break;
            }
            pHeadLong = pHeadLong.next;
            pHeadShort = pHeadShort.next;
        }
        return pHeadLong;

    }

    public int getListLength(ListNode head) {
        int len = 0;
        ListNode ptr = head;
        while (ptr != null) {
            ++len;
            ptr = ptr.next;
        }
        return len;
    }