LeetCode: Swap Nodes in Pairs

一次过

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ListNode *p, *q, *end, *pPre, *pNext;
        p = head;
        q = NULL;
        while (p) {
            end = pPre = p;
            if (p->next) p = p->next;
            else break;
            pNext = p->next;
            p->next = pPre;
            pPre = p;
            p = pNext;
            end->next = p;
            if (!q) head = pPre;
            else q->next = pPre;
            q = end;
        }
        return head;
    }
};

 C#

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode SwapPairs(ListNode head) {
        ListNode p = head, q = null, end = head, pPre = head, pNext = null;
        while (p != null) {
            end = pPre = p;
            if (p.next != null) p = p.next;
            else break;
            pNext = p.next;
            p.next = pPre;
            pPre = p;
            p = pNext;
            end.next = p;
            if (q == null) head= pPre;
            else q.next = pPre;
            q = end;
        }
        return head;
    }
}