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Grokking the Coding Interview Patterns

Middle of the Linked List

Understand how to locate the middle node in a singly linked list by applying fast and slow pointer techniques. This lesson guides you through handling even and odd length lists to solve this common coding interview problem efficiently.

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Statement

Given the head of a singly linked list, return the middle node of the linked list. If the number of nodes in the linked list is even, there will be two middle nodes, so return the second one.

Constraints:

Let n be the number of nodes in a linked list.

  • 1≤1 \leq n ≤100\leq 100
  • 1≤1 \leq Node.value ≤100\leq 100
  • head ≠\neq NULL

Examples

Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Middle of the Linked List

1.

What is the output if the following linked list is given as input?

2 → 4 → 6 → 8 → 10 → NULL

A.

4

B.

6

C.

2

D.

8

1 / 3

Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
2
3
4

Try it yourself

Implement your solution in the following coding playground.

Java
usercode > Solution.java
// Definition for a Linked List node
// class ListNode {
//     int val;
//     ListNode next;
//     // Constructor
//     public ListNode(int val) {
//         this.val = val;
//         this.next = null;
//     }
// }
import ds_v1.LinkedList.ListNode;
import java.util.*;
public class Solution{
    public static ListNode middleNode(ListNode head) {
    
        // Replace this placeholder return statement with your code
        return head;
    }
}
Middle of the Linked List