24. Swap Nodes in Pairs

Medium (Trung bình) C++ 🔗 Xem trên LeetCode

📋 Đề Bài

Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e., only nodes themselves may be changed.)

 

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

🧠 Thuật Toán & Kỹ Thuật

Linked List (Danh sách liên kết)
⏱️ Thời gian O(n²)
💾 Không gian O(n)

💻 Lời Giải

C++ 0024-swap-nodes-in-pairs.cpp 
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        vector<int> v;
        ListNode *currNode = head;
        
        while (currNode) {
            v.push_back(currNode->val);
            currNode = currNode->next;
        }
        
        int n = (int)v.size();
        
        for (int i = 0; i < n; i += 2) {
            if (i + 1 < n) {
                swap(v[i + 1], v[i]);
            }
        }
        
        ListNode *newNode = new ListNode(0);
        ListNode *tmpNode = newNode;
        
        for (int i = 0; i < n; ++i) {
            tmpNode->next = new ListNode(v[i]);
            tmpNode = tmpNode->next;
        } 
        
        return newNode->next;
    }
};