LeetCode 24. 两两交换链表中的节点

迭代

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
         if(head==nullptr || head->next ==nullptr){
             return head;
         }
         ListNode* res = new ListNode();
         res->next = head;
         ListNode* cur = res;
         while(cur->next!=nullptr&&cur->next->next!=nullptr){
            ListNode* p = cur->next;
            ListNode* q = (cur->next)->next;
            ListNode* temp = q->next;
            cur->next = q;
            q->next = p;
            p->next = temp;
            cur = p;
         }
         return res->next;
    }
};

递归

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