解释c++中的 list.swap

在 C++ STL 中，`list` 是一个双向链表容器，它提供了 `swap` 方法用于交换两个列表的内容。具体来说，`list.swap` 方法接受一个参数，表示要与当前列表交换内容的另一个列表。它会将两个列表的内容进行交换，但不会改变它们的大小（即容量不变）。例如：

#include <iostream>
#include <list>

int main() {
    std::list<int> list1 = {1, 2, 3};
    std::list<int> list2 = {4, 5, 6};

    list1.swap(list2);  // 交换 list1 和 list2 的内容

    std::cout << "list1: ";
    for (auto x : list1) {
        std::cout << x << " ";
    }
    std::cout << std::endl;

    std::cout << "list2: ";
    for (auto x : list2) {
        std::cout << x << " ";
    }
    std::cout << std::endl;

    return 0;
}

输出结果为：

list1: 4 5 6
list2: 1 2 3

需要注意的是，`list.swap` 方法的时间复杂度是 O(1)，因为它只是交换了两个指针，而不需要对列表中的元素进行复制或移动。

相关问题

C++ list的Swap实现

C++ 中的 std::list 没有 Swap 函数，但是可以通过编写代码实现两个 std::list 之间的交换。下面是一个示例：

#include <iostream>
#include <list>

using namespace std;

int main()
{
    list<int> a = {1, 2, 3, 4};
    list<int> b = {5, 6, 7, 8};

    a.swap(b);

    cout << "a: ";
    for(auto& i : a)
        cout << i << " ";
    cout << endl;

    cout << "b: ";
    for(auto& i : b)
        cout << i << " ";
    cout << endl;

    return 0;
}

输出结果：

a: 5 6 7 8
b: 1 2 3 4

可以看到，通过 std::list 的成员函数 swap，可以将两个链表进行互换。

#include<iostream> using namespace std; struct LinkedList { // todo: some variables here void initialize() { int n; scanf("%d", &n); int *a = new int[n]; for(int i = 0; i < n; i++) scanf("%d", &a[i]); // todo delete[] a; } void insert(int i, int x) { // todo } void erase(int i) { // todo } void swap() { // todo } void moveback(int i, int x) { // todo } int query(int i) { // todo } void printAll() { // todo } void ClearMemory() { // todo } }; int main() { LinkedList List; int m, op, i, x; List.initialize(); scanf("%d", &m); while(m--) { scanf("%d", &op); if(op == 1) { scanf("%d%d", &i, &x); List.insert(i, x); } else if(op == 2) { scanf("%d", &i); List.erase(i); } else if(op == 3) { List.swap(); } else if(op == 4) { scanf("%d%d",&i, &x); List.moveback(i, x); } else if(op == 5) { scanf("%d", &i); printf("%d\n", List.query(i)); } else if(op == 6) { List.printAll(); } } List.ClearMemory(); return 0; }

抱歉，上述代码并没有实现您的要求，只是一个模版代码。以下是根据您的要求修改后的代码实现单链表：

#include<iostream> 
using namespace std;

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

class LinkedList {
private:
    ListNode *head, *tail;
    int size;
public:
    LinkedList(): head(NULL), tail(NULL), size(0) {}
    void initialize() {
        int n;
        scanf("%d", &n);
        for(int i = 0; i < n; i++) {
            int x;
            scanf("%d", &x);
            ListNode *node = new ListNode(x);
            if(head == NULL) {
                head = tail = node;
            }
            else {
                tail->next = node;
                tail = node;
            }
            size++;
        }
    }
    void insert(int i, int x) {
        if(i < 0 || i > size) return;
        ListNode *node = new ListNode(x);
        if(i == 0) {
            node->next = head;
            head = node;
            if(tail == NULL) tail = head;
        }
        else if(i == size) {
            tail->next = node;
            tail = node;
        }
        else {
            ListNode *cur = head;
            for(int j = 0; j < i - 1; j++) {
                cur = cur->next;
            }
            node->next = cur->next;
            cur->next = node;
        }
        size++;
    }
    void erase(int i) {
        if(i < 0 || i >= size) return;
        ListNode *cur = head, *pre = NULL;
        for(int j = 0; j < i; j++) {
            pre = cur;
            cur = cur->next;
        }
        if(pre == NULL) {
            head = head->next;
            if(head == NULL) tail = NULL;
        }
        else {
            pre->next = cur->next;
            if(pre->next == NULL) tail = pre;
        }
        delete cur;
        size--;
    }
    void swap() {
        if(size <= 2) return;
        ListNode *cur = head, *pre = NULL;
        while(cur && cur->next) {
            ListNode *tmp = cur;
            cur = cur->next;
            tmp->next = cur->next;
            cur->next = tmp;
            if(pre) pre->next = cur;
            pre = tmp;
            cur = tmp->next;
        }
        if(size % 2 == 0) tail = pre;
    }
    void moveback(int i, int x) {
        if(i <= 0 || i > size) return;
        ListNode *cur = head, *pre = NULL;
        for(int j = 0; j < i - 1; j++) {
            pre = cur;
            cur = cur->next;
        }
        for(int j = 0; j < x; j++) {
            if(cur == NULL) cur = head;
            ListNode *tmp = cur->next;
            if(pre == NULL) {
                head = tmp;
                tail->next = cur;
                cur->next = NULL;
                tail = cur;
            }
            else if(tmp == NULL) {
                pre->next = NULL;
                tail = pre;
                cur->next = head;
                head = cur;
            }
            else {
                pre->next = tmp;
                cur->next = tmp->next;
                tmp->next = cur;
            }
            pre = cur;
            cur = cur->next;
        }
    }
    int query(int i) {
        if(i < 1 || i > size) return -1;
        ListNode *cur = head;
        for(int j = 1; j < i; j++) {
            cur = cur->next;
        }
        return cur->val;
    }
    void printAll() {
        ListNode *cur = head;
        while(cur) {
            printf("%d ", cur->val);
            cur = cur->next;
        }
        printf("\n");
    }
    void clearMemory() {
        ListNode *cur = head;
        while(cur) {
            ListNode *tmp = cur;
            cur = cur->next;
            delete tmp;
        }
        head = tail = NULL;
        size = 0;
    }
};

int main() {
    LinkedList list;
    int m, op, i, x;
    list.initialize();
    scanf("%d", &m);
    while(m--) {
        scanf("%d", &op);
        if(op == 1) {
            scanf("%d%d", &i, &x);
            list.insert(i, x);
        }
        else if(op == 2) {
            scanf("%d", &i);
            list.erase(i);
        }
        else if(op == 3) {
            list.swap();
        }
        else if(op == 4) {
            scanf("%d%d", &i, &x);
            list.moveback(i, x);
        }
        else if(op == 5) {
            scanf("%d", &i);
            printf("%d\n", list.query(i));
        }
        else if(op == 6) {
            list.printAll();
        }
    }
    list.clearMemory();
    return 0;
}