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Problem

Swap Nodes in Pairs

LeetCode #24Medium
Three arrows per pair · dummy head

Given the head of a singly linked list, swap every two adjacent nodes and return the new head. You must swap the actual nodes rather than just their values.

Asked atAmazonMicrosoftBloomberg
step 1 / 11
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Shortcut · swap values
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1given head
2cur = head
3while cur and cur.next:
4    swap(cur.val, cur.next.val); cur = cur.next.next
5return head   // usually not allowed!
state
  • goal2 1 4 3

line 1Swap every adjacent pair: (1,2) then (3,4). Cheeky shortcut: leave the nodes alone and swap the VALUES inside them.