LeetCode/24.cpp at master · nitin-maharana/LeetCode · GitHub

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/*
 * Written by Nitin Kumar Maharana
 * nitin.maharana@gmail.com
 */

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
    void swapPairsUtil(ListNode *head)
    {
        ListNode *temp;

        while(head->next && head->next->next)
        {
            temp = head->next;
            head->next = temp->next;
            temp->next = head->next->next;
            head->next->next = temp;
            head = temp;
        }
    }
public:
    ListNode* swapPairs(ListNode* head) {
        if(!head || !head->next)
            return head;

        ListNode* newHead = new ListNode(0);
        newHead->next = head;

        swapPairsUtil(newHead);

        return newHead->next;
    }
};