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  • Swap Nodes in Pairs

    Swap Nodes in Pairs

    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.

    分析: 比较简单的链表操作 需要将a->b->(b->next) 转换为b->a->(b->next)这样的形式

    自己写的代码为

    /**
     * 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 ==nullptr || head->next ==nullptr)
                return head;
            ListNode* cur = head;
            ListNode* curNext = cur->next;
            cur->next = curNext->next;
            curNext->next = cur;
            head= curNext;
            ListNode* prev = cur;
            while(prev && prev->next){
                cur = prev->next;
                curNext = cur->next;
                if(curNext){
                     cur->next = curNext->next;
                     curNext->next = cur;
                     prev->next = curNext;
                     prev = cur;
                }else{
                    cur->next =curNext;
                    prev = nullptr;
                }
                
            }
            return head;
        }
    };

    Discuss中提出的用指针的指针解决方案,稍微难一点,但很高效

    ListNode* swapPairs(ListNode* head) {
        ListNode **pp = &head, *a, *b;
        while ((a = *pp) && (b = a->next)) {
            a->next = b->next;
            b->next = a;
            *pp = b;
            pp = &(a->next);
        }
        return head;
    }
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  • 原文地址:https://www.cnblogs.com/willwu/p/6135411.html
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