力扣 160 相交链表 快慢指针 双指针

[题目链接](https://leetcode-cn.com/problems/intersection-of-two-linked-lists/)

思路一

    // 思路一，hashmap记录hashcode，没有重写的hashcode都与内存地址有关，所以这样是可以的。
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        HashMap<Integer, Boolean> map = new HashMap<>();
        while (headA != null) {
            map.put(headA.hashCode(), true);
            headA = headA.next;
        }

        while (headB != null) {
            if (map.get(headB.hashCode()) == null) {
                map.put(headB.hashCode(), true);
            }
            else {
                return headB;
            }
            headB = headB.next;
        }
        return null;
    }

思路二来自

    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        ListNode pA = headA;
        ListNode pB = headB;

        while (pA != pB) {
            pA = pA == null ? headA : pA.next;
            pB = pB == null ? headA : pB.next;
            pB = pB == null ? headA : pB.next;
        }

        return pA;
    }