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Can you explain how to split a linked list into two halves?

To split a linked list into two halves, you need to find the middle node and then separate the list at that point.

In more detail, splitting a linked list into two halves involves traversing the list to find the middle node, then breaking the list into two separate lists at that point. This process can be achieved using a slow and fast pointer approach, also known as the hare and tortoise method. For more about linked lists, see the dynamics of linked lists.

Firstly, initialise two pointers, slow and fast, at the head of the linked list. The slow pointer moves one step at a time, while the fast pointer moves two steps at a time. By the time the fast pointer reaches the end of the list, the slow pointer will be at the middle of the list. This is because the fast pointer is moving at twice the speed of the slow pointer.

Once the middle of the list is found, the next step is to split the list into two halves. This can be done by setting the next pointer of the slow pointer (which is now at the end of the first half of the list) to null, effectively breaking the link between the two halves of the list. The head of the first half of the list is the original head of the list, and the head of the second half of the list is the next node of the middle node.

Understanding fundamental computer operations can aid in grasping how pointers work within data structures.


It's important to note that if the number of nodes in the linked list is even, there will be two middle nodes. In this case, you can choose either of the two middle nodes as the end of the first half and the start of the second half.

This method of splitting a linked list into two halves is efficient and only requires a single traversal of the list. It's a common technique used in many algorithms, such as the merge sort algorithm for linked lists. For a deeper understanding, explore standard algorithms and the concept of ADT.

IB Computer Science Tutor Summary: To split a linked list into two halves, use two pointers: one moves twice as fast as the other. When the fast pointer reaches the end, the slow pointer is in the middle. Break the list at this point to create two separate lists. This efficient method is often used in algorithms like merge sort for linked lists.

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