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Grokking the Coding Interview Patterns in C++

Middle of the Linked List

Understand and implement the fast and slow pointer approach to find the middle node of a singly linked list. This lesson guides you through solving the problem efficiently, including the case when the list has an even number of nodes, returning the second middle node.

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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.

C++
usercode > Solution.cpp
// Definition for a Linked List node
// class ListNode {
// public:
//     int val;
//     ListNode* next;
//     // Constructor
//     ListNode(int val = 0, ListNode* next = nullptr);
// };
ListNode* GetMiddleNode(ListNode* head){
    // Replace this placeholder return statement with your code
    return head;
}
Middle of the Linked List