LeetCode 24. Swap Nodes in Pairs C++ Solution

/**
 * 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) {
        if(head == NULL || head->next == NULL){
            return head;
        }
        ListNode* next = head->next;
        ListNode* answer = head->next;
        
        head->next = next->next;
        next->next = head;
        
        next = head->next;
        while(head->next != NULL && next->next != NULL){
            next = head->next;
            head->next = next->next;
            head = head->next;
            next->next = head->next;
            head->next = next;
            
            head = head->next;
            next = head->next;
        }
        
        return answer;
    }
};

노드만으로 해결