Swap Nodes in Pairs
Medium
Topics
Given the head of a linked list, swap every two adjacent nodes and return its head. You must swap the nodes themselves, not just their values. A trailing odd node stays in place.
Example 1
Input: head = [1,2,3,4] Output: [2,1,4,3]
Example 2
Input: head = [1,2,3] Output: [2,1,3]
Constraints
- 0 <= number of nodes <= 100
- 0 <= Node.val <= 100
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