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Editor to share with you how LeetCode solves the node problem in the pairwise exchange list, I believe most people don't know much about it, so share this article for your reference. I hope you can learn a lot after reading this article. Let's learn about it together.

Meaning of the title

Given a linked list, the adjacent nodes in the list are exchanged and the exchanged list is returned. You can't just change the value inside the node, but you need to actually exchange the node.

Sample

Given 1-> 2-> 3-> 4, you should return 2-> 1-> 4-> 3.

Recursive method of problem solving:

Recursion starts with the header node head of the linked list.

Each recursion is responsible for exchanging a pair of nodes. The two nodes to be exchanged are represented by firstNode and secondNode.

The next recursion passes the next pair of nodes that need to be swapped. If there are nodes in the linked list, continue recursion.

After swapping two nodes, secondNode is returned because it is the new header after the exchange.

After all the nodes have been exchanged, we return the exchanged header, which is actually the second node of the original linked list.

Class Solution {public ListNode swapPairs (ListNode head) {/ / If the list has no node or has only one node left.if ((head = = null) | | (head.next = = null) {return head;} / / Nodes to be swappedListNode firstNode = head;ListNode secondNode = head.next;// SwappingfirstNode.next = swapPairs (secondNode.next); secondNode.next = firstNode;// Now the head is the second nodereturn secondNode;}} time complexity: O (N), where NN refers to the number of nodes in the linked list. Space complexity: O (N), stack space used by recursive procedures.

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