编写一个程序，找到两个单链表相交的起始节点。

public class FindIntersect {

    /**
     * 思路：
     *      先求出两链表的长度，然后让更长的那个移动到能和更短的那个一样长的位置
     *      然后两个一起移动，直到值相等，说明相交了
     * @param headA
     * @param headB
     * @return 相交的节点
     */
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        int lenA = 0;
        ListNode temp = headA;
        while (temp != null) {
            temp = temp.next;
            lenA++;
        }
        int lenB = 0;
        temp = headB;
        while (temp != null) {
            temp = temp.next;
            lenB++;
        }
        if (lenA > lenB) {
            for (int i = 0; i < lenA - lenB; i++)
                headA = headA.next;
        }
        else if (lenA < lenB) {
            for (int i = 0; i < lenB - lenA; i++)
                headB = headB.next;
        }

        while (headA != null && headB != null) {
            if (headA == headB) {
                break;
            }
            headA = headA.next;
            headB = headB.next;
        }

        if (headA == null || headB == null)
            return null;
        return headA;
    }

}