LeetCode-160~Intersection of Two Linked Lists

Write a program to find the node at which the intersection of two singly linked lists begins.
For example, the following two linked lists:

图一：举例

begin to intersect at node c1.
Notes:

• If the two linked lists have no intersection at all, return null.
• The linked lists must retain their original structure after the function returns.
• You may assume there are no cycles anywhere in the entire linked structure.
• Your code should preferably run in O(n) time and use only O(1) memory.

算法分析

方法一：

将链表A加入到set中，检测链表B中的每一个节点是否在set中。

Java代码

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        Set<ListNode> aListNode = new HashSet<>();
        while (headA != null) {
            aListNode.add(headA);
            headA = headA.next;
        }
        while (headB != null) {
            if (aListNode.contains(headB)) return headB;
            else headB = headB.next;
        }
        return null;
    }
}