ARST打卡第222周[222/521]

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58

// g++ A.cpp -g -o A.out -std=c++11
#include <bits/stdc++.h>
using namespace std;

struct ListNode {
    int val;
    ListNode *next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode *next) : val(x), next(next) {}
};

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        if (!head || !head->next) {
            return head;
        }
        ListNode* l = head;
        ListNode* r = head->next;
        
        // 先保留向下的箭头，然后从向下的这里开始修改即可
        ListNode* next_l = r->next;
        r->next = l;
        l->next = next_l;
        head = r;

        // 这里 l 左已经变到后面了
        ListNode* dummy_head = l;
        // 手贱，写多了感叹号，然后调试的时候就说为啥直接退出或者一直运行不到while...
        // while (!next_l && !next_l->next) {
        while (next_l && next_l->next) {
            l = next_l;
            r = next_l->next;
            next_l = r->next;
            r->next = l;
            l->next = next_l;
            dummy_head->next = r;
            dummy_head = l;
        }

        return head;
    }
};

int main() {
    Solution sol;
    ListNode* test = new ListNode(1);
    test->next = new ListNode(2);
    test->next->next = new ListNode(3);
    test->next->next->next = new ListNode(4);
    ListNode* out = sol.swapPairs(test);
    while (out) {
        cout << out->val << endl;
        out = out->next;
    }
    return 0;
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        ListNode* dummyHead = new ListNode(0);
        dummyHead->next = head;
        ListNode* temp = dummyHead;
        while (temp->next != nullptr && temp->next->next != nullptr) {
            ListNode* node1 = temp->next;
            ListNode* node2 = temp->next->next;
            temp->next = node2;
            node1->next = node2->next;
            node2->next = node1;
            temp = node1;
        }
        return dummyHead->next;
    }
};
链接：https://leetcode.cn/problems/swap-nodes-in-pairs/solutions/444474/liang-liang-jiao-huan-lian-biao-zhong-de-jie-di-91/