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$ curl repovive.com/roadmaps/data-structures/linked-lists/finding-the-middle

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Repovive

Finding the Middle - Linked Lists | Data Structures | Repovive

Repovive.

Data Structures19 sections · 729 units49h total

Open in Course

Finding the Middle

Fast-slow technique

To find the middle node:

slow = head
fast = head
while fast != null and fast.next != null:
    slow = slow.next
    fast = fast.next.next
return slow

For odd-length lists, slow points to the exact middle. For even-length lists, it points to the second of the two middle nodes.

If you need the first middle node for even-length lists, check fast.next != null and fast.next.next != null instead.

Why is this useful? Many problems require processing the two halves of a list separately. Finding the middle in $O(n)$ time and $O(1)$ space enables this without converting to an array first.