LeetCode 24 Swap Nodes in Pairs

Source: Internet
Author: User

LeetCode 24 Swap Nodes in Pairs

Given a linked list, swap every two adjacent nodes and return its header. For example, given 1-> 2-> 3-> 4, you should return 2-> 1-> 4-> 3. Your algorithm must use a unique and unchanged space. You cannot modify the values in the list. Only nodes can be changed.
Give a linked list, swap every two adjacent nodes and return its head.For example, Given 1->2->3->4, you should return the list as 2->1->4->3.Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

Let's take the 1, 2, 3, and 4 given in the question as an example and take them as two parts.

1,2 -- 3,4

Or I can draw a picture to make it more intuitive ......

/** * 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) return NULL;        if(head->next == NULL) return head;        ListNode* temp = head->next;        head->next = swapPairs(temp->next);        temp->next = head;        return temp;    }};


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