Description

Middle of the Linked List - LeetCode

Given the head of a singly linked list, return the middle node of the linked list.

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

Example 1:

Input: head = [1,2,3,4,5]
Output: [3,4,5]
Explanation: The middle node of the list is node 3.

Example 2:

Input: head = [1,2,3,4,5,6]
Output: [4,5,6]
Explanation: Since the list has two middle nodes with values 3 and 4, we return the second one.

Constraints:

• The number of nodes in the list is in the range [1, 100].
• 1 <= Node.val <= 100

Solution

• 노드가 몇 개 있는 지 먼저 확인하고 길이의 반만큼만 head를 움직였다.

// second attempt on 083021
    public ListNode middleNode2(ListNode head) {
        int length = 1;
        ListNode temp = head;
        while (temp.next != null) {
            temp = temp.next;
            length++;
        }

        for (int i = 0; i < length / 2; i++) {
            head = head.next;
        }

        return head;
    }

• 솔루션을 보니 fast, slow를 두고 풀었다. 전에 유툽에서 이런식으로 노드의 중간을 알아내는 게 생각났다.

// using fast and slow pointer
    public ListNode middleNode3(ListNode head) {
        ListNode fast = head, slow = head;
        while (fast != null && fast.next != null) {
            fast = fast.next.next;
            slow = slow.next;
        }
        return slow;
    }