算法题：找到两个单链表相交的起始节点（假设链表无环）

问：找到两个单链表相交的起始节点（假设链表无环）：

public class ListNode {
    int val;
    ListNode next;

    ListNode(int x) {
        val = x;
        next = null;
    }
}

public class Main {
    public static ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        ListNode pa = headA, pb = headB;
        while (pa != pb) {
            pa = (pa != null) ? pa.next : headB;
            pb = (pb != null) ? pb.next : headA;
        }
        return pa;
    }

    public static void main(String[] args) {
        // 创建两个链表
        ListNode listA = new ListNode(1);
        listA.next = new ListNode(2);
        listA.next.next = new ListNode(3);

        ListNode listB = new ListNode(4);
        listB.next = listA.next;  // 使得两个链表相交于节点2

        ListNode intersectionNode = getIntersectionNode(listA, listB);
        System.out.println(intersectionNode.val);  // 2
    }
}