visualization

Linked List Reversal

Three pointers, one flip per node, zero extra memory.

list = 3 → 7 → 1 → 9 → 4 · reverse in placestep 1/17

Start: every arrow points right, head is 3. prev is None and cur sits on 3.

pseudocode

prev = None
cur = head
while cur:
    next = cur.next      # save the escape route
    cur.next = prev      # flip the arrow
    prev, cur = cur, next
 
return prev              # new head