Swap Nodes in Pairs

Swap Nodes in Pairs

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Question  Solution 

Total Accepted: 62382  Total Submissions: 192595  Difficulty: Medium

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.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
		
		if( !head || !head->next )
			return head;
		ListNode * Node_cur = head;
		ListNode * t_head = head->next;
		ListNode * Node_pre = head;
		Node_cur->next = t_head->next;
		t_head->next = Node_cur;
		Node_cur = Node_pre->next;
		while( Node_cur && Node_cur->next)
		{
			Node_pre->next = Node_cur->next;
			Node_cur->next = Node_cur->next->next;
			Node_pre->next->next = Node_cur;
			Node_pre = Node_cur;
			Node_cur = Node_cur->next;
		}
		return t_head;
    }
};