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Swap Nodes in Pairs Test | Pre-employment assessment - Testlify
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Swap Nodes in Pairs Test

Overview of Swap Nodes in Pairs Test

The goal of the problem is to swap two adjacent elements in the list and return the head of the resulted list.

Skills measured

  • Two pointers
  • Linked list

Available in



Coding Test


25 Mins





Use of Swap Nodes in Pairs test

The solution approach to the problem is to swap adjacent pairs of nodes in a linked list.
Let there be a funtion named as 'swapPairs' which takes a pointer to the head of a linked list head as input and returns a pointer to the head of the modified linked list.
The function creates a new node pre with a value of 0 and sets its next pointer to the head of the linked list. This node will be used as a dummy node to handle the case where the head itself needs to be swapped.
The function declares two pointers cur and tmp and initializes cur to the pre node. The cur pointer will be used to iterate through the linked list and swap adjacent pairs of nodes.
The while loop runs as long as cur->next and cur->next->next are not nullptr, indicating that there are at least two more nodes to swap.
Inside the while loop, the pointer tmp is assigned to cur->next, representing the first node of the current pair to be swapped.
The next pointer of cur is updated to cur->next->next, effectively skipping the second node of the current pair.
The next pointer of tmp is updated to tmp->next->next, effectively skipping the nodes after the second node of the current pair.
The next pointer of cur->next is updated to tmp, linking the second node of the current pair to the first node.
The cur pointer is updated to tmp, moving it forward to the next pair of nodes.
Once the while loop finishes, the swapping process is completed, and the modified linked list is obtained.
Finally, the function returns pre->next, which represents the head of the modified linked list.

Relevant for

  • Software Developer Engineer
  • Software Developer
  • Software Engineer

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Two pointers

In the "Swap Nodes in Pairs" problem, the two pointers skill involves using two pointers to traverse the linked list and swap pairs of nodes. One pointer points to the current node being processed, while the other pointer points to the previous node. By updating the pointers and swapping the nodes in pairs, we can efficiently rearrange the linked list. This skill is important as it allows us to perform the swapping operation in a single pass through the linked list, reducing the time complexity of the algorithm and improving its efficiency.


Linked list

In the "Swap Nodes in Pairs" problem, a linked list skill is utilized to swap every two adjacent nodes in a given linked list. This skill is important as it helps in efficiently rearranging the nodes in a linked list, which can be useful in various scenarios such as optimizing the performance of certain algorithms or improving the readability of the list. By understanding and implementing this skill, one can improve their ability to manipulate linked list structures and solve complex problems involving linked lists more effectively.

The Swap Nodes in Pairs test is created by a subject-matter expert

Testlify’s skill tests are designed by experienced SMEs (subject matter experts). We evaluate these experts based on specific metrics such as expertise, capability, and their market reputation. Prior to being published, each skill test is peer-reviewed by other experts and then calibrated based on insights derived from a significant number of test-takers who are well-versed in that skill area. Our inherent feedback systems and built-in algorithms enable our SMEs to refine our tests continually.

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