24. Swap Nodes in Pairs.cpp

/*Swap Nodes in Pairs:Given a linked list, swap every two adjacent nodes and return its head.*/
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        if(head == NULL || head->next == NULL) return head;
        ListNode* tmp = head->next;
        head->next = swapPairs(tmp->next);
        tmp->next = head;
        return tmp;
    }
};