两个链表的第一个公共节点

public Node firstCommonNode(Node a, Node b){
    Node l1 = a;
    Node l2 = b;
    while(l1 != l2){
        l1 = (l1 == null) ? b : l1.next;
        l2 = (l2 == null) ? a : l2.next;
    }
    return l1;
}