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Problem

Reverse Linked List

LeetCode #206Easy
Flip every arrow · prev / curr / next

Given the head of a singly linked list, reverse the list and return the new head.

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step 1 / 17
∅
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Iterative · three pointers
▸
1prev ← ∅;  curr ← head
2while curr:
3    next ← curr.next      // save the rest
4    curr.next ← prev      // flip the arrow
5    prev ← curr; curr ← next
6return prev               // new head
state
  • prev∅
  • currhead (1)

line 1Reverse the list in place. Keep three pointers: prev (the part already reversed, starts at ∅), curr (the node we are flipping), and next (a temporary so we don’t lose the tail).