How to Fix Middle of Linked List Errors

In this tutorial, you'll learn about How to Fix Middle of Linked List Errors. We cover key concepts, practical examples, and best practices.

Fix middle of linked list errors when slow-fast advances incorrectly or even-length returns wrong middle.

Quick Fix

Wrong

def middle(h):
    n=0; c=h
    while c: n+=1; c=c.next
    c=h
    for _ in range(n//2): c=c.next
    return c

Two passes required. Fails read-once scenarios.

Right

def middle(h):
    s=f=h
    while f and f.next:
        s=s.next; f=f.next.next
    return s

1->2->3->4->5 -> 3. 1->2->3->4->5->6 -> 4. O(n).

Prevention

Slow-fast: slow 1 step, fast 2. Second middle for even length.

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