丙加·第10章·答案

#include <iostream>
#include <string>
#include <map>
#include <sstream>
#include <vector>
#include <algorithm>
#include <cctype>

int main() {
    std::string text;
    std::cout << "Please input the English text: ";
    std::getline(std::cin,text);

    // 将标点替换为空格
    // 排除'和-
    std::replace_if(text.begin(), text.end(),
        [](char c) { 
            return std::ispunct(c) && c != '-' && c != '\'';
        }, ' ');

    // 转换为小写并分词
    std::transform(text.begin(), text.end(), text.begin(), ::tolower);
    std::stringstream ss(text);
    std::string word;

    std::map<std::string, int> wordCount;

    // 统计词频
    while (ss >> word) {
        if (!word.empty()) {
            wordCount[word]++;
        }
    }

    // 按字母顺序输出
    std::cout << "Result：" << std::endl;
    for (const auto& pair : wordCount) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    return 0;
}

Please input the English text: Hi hi.Hi...HI Bye I'm Good thaNKs.AnD yOU?
Result：
and: 1
bye: 1
good: 1
hi: 4
i'm: 1
thanks: 1
you: 1

#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<tuple>

using namespace std;

struct Student{
    string name;
    int score;
    string id;
};

int main(){
    vector<Student> students={
        // 或者 make_tuple("Alice",85,"001"),
        {"Alice",85,"001"},
        {"Bob",92,"002"},
        {"Charlie",78,"003"},
        {"David",95,"004"},
    };

    sort(students.begin(),students.end(),
        [](const Student& a,const Student& b){
            return a.score > b.score;
        });

    cout<<"Sort results by grade: "<<endl;
    for(const auto& student : students){
        cout << student.name <<"-Grade: "<<student.score<<" ID:"<<student.id<<endl;
    }

    string search_name;
    cout<<"\nPlease enter the name of the student you want to search for:";
    cin>>search_name;

    auto it = find_if(students.begin(),students.end(),
                    [&](const Student& s){
                        return s.name == search_name;
                    });
    if(it != students.end()){
        cout<<"Find student: "<<it->name
        <<",grade: "<<it->score
        <<",ID: "<<it->id<<endl;
    }else{
        cout<<"Not found: "<<search_name<<endl;
    }

    return 0;
}

#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <iterator>

int main() {
    std::vector<int> numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 2, 6, 7, 1, 0};

    std::cout << "Origin: ";
    for (int num : numbers) std::cout << num << " ";
    std::cout << std::endl;

    // 过滤偶数
    auto it = std::remove_if(numbers.begin(), numbers.end(), 
        [](int x) { return x % 2 == 0; });
    numbers.erase(it, numbers.end());

    std::cout << "Even filtered: ";
    for (int num : numbers) std::cout << num << " ";
    std::cout << std::endl;

    // 每个元素平方
    std::transform(numbers.begin(), numbers.end(), numbers.begin(),
        [](int x) { return x * x; });

    std::cout << "Squared: ";
    for (int num : numbers) std::cout << num << " ";
    std::cout << std::endl;

    // 去重
    std::sort(numbers.begin(), numbers.end());
    auto last = std::unique(numbers.begin(), numbers.end());
    numbers.erase(last, numbers.end());

    std::cout << "Uniqued: ";
    for (int num : numbers) std::cout << num << " ";
    std::cout << std::endl;

    // 求和
    int sum = std::accumulate(numbers.begin(), numbers.end(), 0);

    std::cout << "Sum: " << sum << std::endl;

    return 0;
}

#include <iostream>
#include <memory>

class Resource {
public:
    Resource(int id) : id(id) {
        std::cout << "Creating Resource " << id << std::endl;
    }
    ~Resource() {
        std::cout << "Destroying Resource " << id << std::endl;
    }
    void use() {
        std::cout << "Using Resource " << id << std::endl;
    }
private:
    int id;
};

class NodeA;
class NodeB;

class NodeA {
public:
    // 错误1：未弱化的循环引用
    // std::shared_ptr<NodeB> b_ptr;、
// 修改：
    std::weak_ptr<NodeB> b_ptr;
    ~NodeA() { std::cout << "NodeA destroyed" << std::endl; }
};

class NodeB {
public:
    // 错误1：未弱化的循环引用
    // 不过改 NodeA 一处就好了
    // 当然也可以像由崎夫妇一样两边都弱化
    std::shared_ptr<NodeA> a_ptr;
    ~NodeB() { std::cout << "NodeB destroyed" << std::endl; }
};

void test_smart_pointers() {
    // 错误2：多个unique_ptr管理同一个对象
    int* raw_ptr = new int(42);
    std::unique_ptr<int> up1(raw_ptr);
// 修改：
// 要么不要这个多重管理，要么采用 shared_ptr，
// 要么创建俩对象
    // std::unique_ptr<int> up2(raw_ptr);

    // 错误3：使用已释放的unique_ptr
    std::unique_ptr<Resource> r1(new Resource(1));
    std::unique_ptr<Resource> r2 = std::move(r1);
    // r1->use();  
// 修改：
    if (r1 != nullptr){
        r1->use();
    }

    // 循环引用实例
    // 已经在上面类定义中弱化了引用。
    auto nodeA = std::make_shared<NodeA>();
    auto nodeB = std::make_shared<NodeB>();
    nodeA->b_ptr = nodeB;
    nodeB->a_ptr = nodeA;

    // 错误4：错误的数组删除
    // std::unique_ptr<int> arr_ptr(new int[10]);
// 修改：
    std::unique_ptr<int[]> arr_ptr(new int[10]);
// 或者自己写（不推荐）删除函数对象
    // std::unique_ptr<int, void(*)(int*)> arr_ptr(new int[10], [](int* p) { delete[] p; });

    // 错误5：get()误用
    std::shared_ptr<Resource> shared_res = std::make_shared<Resource>(2);
    Resource* raw_res = shared_res.get();
    // delete raw_res;  // 危险！
// 修改：直接删掉这个，不需要手动删除
// 如果非要解除引用（这里是 shared_ptr，可能不会释放），使用shared_res.reset()
// 对于unique_ptr，reset 和 release都可以释放

// 错误6：自管理资源冲突
    // std::shared_ptr<FILE> file_ptr(fopen("test.txt", "w"));
    // fclose(file_ptr.get());  // 危险！
// 修改：使用 fclose 作为释放函数，外边什么都不做
// 还是那句话，**绝对不要** 手动删除 get() 返回的指针！
    std::shared_ptr<FILE> file_ptr(fopen("test.txt", "w"), fclose);
}

int main() {
    test_smart_pointers();
    return 0;
}