LeetCode 24. Swap Nodes in Pairs

Linked List

Given a linked list, swap every two adjacent nodes and return its head.

Example 1:

Input: head = [1,2,3,4]
Output: [2,1,4,3]

Example 2:

Input: head = []
Output: []

Example 3:

Input: head = [1]
Output: [1]

Constraints:

• The number of nodes in the list is in the range [0, 100].

• 0 <= Node.val <= 100

Follow up: Can you solve the problem without modifying the values in the list's nodes? (i.e., Only nodes themselves may be changed.)

Solution:

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中文版解答Bilibili Link

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        if (head == nullptr || head->next == nullptr) {
            return head;
        }
        
        ListNode* new_head = head->next;
        
        head->next = swapPairs(new_head->next);
        new_head->next = head;
        
        return new_head;
    }
};