/*** 两个链表的第一个公共节点* <p>* 先计算两个链表的长度，让长的链表先走两个链表的差值，然后一起走，比较相等** @param l1* @param l2* @return*/public ListNode findFirstCommonNode(ListNode l1, ListNode l2) {if (null == l1 || null == l2) return null;int size1 = 0;ListNode head = l1;while (head != null) {size1++;head = head.next;}head = l2;int size2 = 0;while (head != null) {size2++;head = head.next;}if (size1 > size2) {int diff = size1 - size2;while (diff > 0) {diff--;l1 = l1.next;}} else {int diff = size2 - size1;while (diff > 0) {diff--;l2 = l2.next;}}while (l1 != null && l2 != null) {if (l1 == l2) return l1;l1 = l1.next;l2 = l2.next;}return null;}