Karl's Nest
0%

leetcode-day-8

Posted on In
Day-8 Middle of the Linked List

LeetCode 30 days Challenge - Day 8

本系列将对LeetCode新推出的30天算法挑战进行总结记录，旨在记录学习成果、方便未来查阅，同时望为广大网友提供帮助。

Middle of the Linked List

Given a non-empty, singly linked list with head node head, return a middle node of linked list.

If there are two middle nodes, return the second middle node.

Example 1:

1
2
3
4
5
Input: [1,2,3,4,5]
Output: Node 3 from this list (Serialization: [3,4,5])
The returned node has value 3.  (The judge's serialization of this node is [3,4,5]).
Note that we returned a ListNode object ans, such that:
ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.

Example 2:

1
2
3
Input: [1,2,3,4,5,6]
Output: Node 4 from this list (Serialization: [4,5,6])
Since the list has two middle nodes with values 3 and 4, we return the second one.

Note:

  • The number of nodes in the given list will be between 1 and 100.

Solution

题目要求分析：给定一个非空链表的头指针，返回这个链表在中间位置的结点。

解法：

典型例题，常常使用快慢指针来定位链表中部。

快指针一次步进2个结点，慢指针一次步进1个结点。当快指针到达末尾，慢指针正好到达链表中部。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
ListNode* middleNode(ListNode* head) {
    ListNode* fast = head, * slow = head;
    while (fast && fast->next) {
        slow = slow->next;
        fast = fast->next->next;
    }
    return slow;
}

传送门：Middle of the Linked List

Karl