By yusijia

Updated:

Contents

/*

  • Given 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.
    /
    /*
  • Definition for singly-linked list.
  • public class ListNode {
  • int val;
  • ListNode next;
  • ListNode(int x) {
  • val = x;
  • next = null;
  • }
  • }
    */
  • 一对一对的交换位置
  • 另开一个空的新头结点来辅助
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class Solution {  
public:  
    ListNode *swapPairs(ListNode *head) {  
        ListNode *newHead = new ListNode(0);  
        newHead->next = head;  
        ListNode *preNode = newHead, *curNode = head;  
        int cnt = 1;  
        while (curNode != NULL && curNode->next != NULL) {  
            // swap curNode and curNode->next  
            preNode->next = curNode->next;  
            curNode->next = preNode->next->next;  
            preNode->next->next = curNode;  
              
            // go over two nodes  
            preNode = curNode;  
            curNode = curNode->next;  
        }  
        head = newHead->next;  
        delete newHead;  
        return head;  
    }  
};
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