求两个单链表的交点

import java.util.HashSet;
import java.util.Set;

class ListNode {
    int val;
    ListNode next;

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

    ListNode(int x, ListNode next) {
        this.val = x;
        this.next = next;
    }
}

public class Temp {

    public static ListNode getIntersectionNode1(ListNode headA, ListNode headB) {
        if (headA == null || headB == null)
            return null;
        ListNode i = headA;
        ListNode j = headB;
        while (i != j) {
            i = (i == null ? headB : i.next);
            j = (j == null ? headA : j.next);
        }
        return i;
    }

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

    public static ListNode getIntersectionNode2(ListNode headA, ListNode headB) {
        int distance = getListLength(headA) - getListLength(headB);
        if (distance < 0) {
            ListNode temp = headA;
            headA = headB;
            headB = temp;
        }
        distance = Math.abs(distance);
        ListNode currA = headA;
        ListNode currB = headB;
        while (currA != null) {
            if (distance-- > 0) {
                currA = currA.next;
            } else if (currA.val != currB.val) {
                currA = currA.next;
                currB = currB.next;
            } else {
                break;
            }
        }

        return currA;
    }

    public static ListNode getIntersectionNode3(ListNode headA, ListNode headB) {
        if (headA == null || headB == null) {
            return null;
        }

        ListNode intersectionNode = null;

        Set<ListNode> nodes = new HashSet<>();
        ListNode p = headA;
        while (p != null) {
            nodes.add(p);
            p = p.next;
        }

        ListNode curr = headB;
        while (curr != null) {
            if (nodes.contains(curr)) {
                intersectionNode = curr;
                break;
            }
            curr = curr.next;
        }

        return intersectionNode;
    }

    public static void main(String[] args) {
        ListNode _6 = new ListNode(6);
        ListNode _2 = new ListNode(2, _6);
        ListNode _3 = new ListNode(3, _6);
        ListNode _1 = new ListNode(1, _2);

        ListNode intersectionNode1 = getIntersectionNode1(_1, _3);
        System.out.println(intersectionNode1.val);

        ListNode intersectionNode2 = getIntersectionNode2(_1, _3);
        System.out.println(intersectionNode2.val);

        ListNode intersectionNode3 = getIntersectionNode3(_1, _3);
        System.out.println(intersectionNode3.val);
    }
}