Swap Nodes in Pairs(24)

/**
 * 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* temp1 = head;
        ListNode* temp2 = head->next;
        ListNode* temp3 = temp2->next;
        temp2->next = temp1;
        temp1->next = swapPairs(temp3);
        return temp2;
    }
};