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Given a linked list, swap every two adjacent nodes and return its head.
You may not modify the values in the list's nodes, only nodes itself may be changed.
Example:
Given1->2->3->4
, you should return the list as2->1->4->3
Method 1. 递归
/**
* 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 *p = head->next;
head->next = swapPairs(head->next->next);
p->next = head;
return p;
}
};
Method 2. 迭代
/**
* 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 * dummy = new ListNode(-1);
dummy->next = head;
ListNode * pre = dummy;
while (pre->next && pre->next->next) {
ListNode *t = pre->next->next;
pre->next->next = t->next;
t->next = pre->next;
pre->next = t;
pre = t->next;
}
return dummy->next;
}
};
完,