真实项目中使用 std::vector，用得最少的操作，就是 insert 或 erase，即：几乎不对一个向量对象做插入和删除操作。那么，std::vector 用得最多的操作是什么呢？

1. 课堂视频

2. 完整代码

#include <cassert>
#include <cmath> // 求绝对值等

#include <iostream>
#include <iomanip>
#include <string>
#include <string_view>
#include <vector>

// 取号机 
class NumberMachine
{
public:
    int Inc() { return ++no; /*前置自增*/ }
private:
    int no = 0; // 成员数据默认初始化
};

// 普通人
class Person
{
public:
    explicit Person(int no); 
    
    Person(Person const& o) // 拷贝构造 
        : no(o.no), name(o.name),
        gender(o.gender), age(o.age),
        height(o.height), weight(o.weight)
    {}          
    
    virtual ~Person() = default; // 默认析构实现

public:
    // 获取各项基本信息的数据
    int GetNo() const { return no; }
    std::string GetName() const { return name; }
    int GetGender() const { return gender; }
    int GetAge() const { return age; }
    int GetHeight() const { return height; }
    int GetWeight() const { return weight; }

    // 赛后感言（落选感言）
    void virtual Speech(std::string_view desc) const
    {
        std::cout << AboutMe()
            << "\n遗憾落选，因为我" << desc
            << "\n感谢大赛，我将越活越美\n";
    }

protected:
    virtual std::string AboutMe() const // 关于
    {
        std::string s = "我是";
        
        s += name + " " + std::to_string(age) + "岁\n"
            + "高 " + std::to_string(height) + " 重 " 
            + std::to_string(weight);
            
        return s;
    }

private:
    int no; // 编号
    std::string name; // 姓名
    int gender; // 性别(0女，1男)
    int age; // 年龄
    int height; // 身高（cm)
    int weight; // 体重（kg）
};

Person::Person(int no)
    : no(no)
{
    std::cout << "\t姓名：";
    std::getline(std::cin, name);
    
    std::cout << "\t性别（0女 1男）：";
    std::cin >> gender;
    
    std::cout << "\t年龄：";
    std::cin >> age;
    
    std::cout << "\t身高（cm）：";
    std::cin >> height;
    
    std::cout << "\t体重（kg）：";
    std::cin >> weight;
}    

// 美女
class Beauty : public Person
{
public:
    explicit Beauty(Person const& p)
        : Person(p)
    {
        std::cout << "\t胸腰臀三围数据（cm，空格间隔）：";
        std::cin >> bust >> waist >> hip;
    }
    
public:
    int GetBust() const { return bust; }
    int GetWaist() const { return waist; }
    int GetHip() const { return hip; }

public:
    // 美女的赛后演讲
    void Speech(std::string_view desc) const override
    {
        std::cout << AboutMe()
            << "\n\n很开心通过海选" 
            << "\n评委评价我：" << desc << "！"
            << "\n感谢认可！"
            << "\n感谢父母给了我好基因！\n";
    }

protected:
    // 美女的自我介绍内容
    std::string AboutMe() const override
    {
        std::string s = Person::AboutMe(); // 继承的应用
        
        s += "\n我的三围："
            + std::to_string(bust) + " "
            + std::to_string(waist) + " "
            + std::to_string(hip);

        return s;
    }

private:
    int bust, waist, hip; // 胸围，腰围，臀围
};

// 报名
Person* SignUp()
{
    // 取号机
    static NumberMachine nm;
    
    std::cout << "【报名】\n"; 
    
    int no = nm.Inc(); // 取号
    return new Person(no); // 构造Person对象，需填写基本信息
}

// 评测结果
struct Result
{
    bool lost; // 为真表示落选
    Person const * contestant; // 选手（普通人或美女）
    std::string desc; // 说明（落选原因或胜选评价）
};

// 生成落选结果
Result OnLost(Person const* p, std::string_view desc)
{
    std::cout << "\t" << p->GetNo() << " 号选手落选\n";
    
    Result r;
    r.lost = true; // 落选
    r.contestant = p;
    r.desc = desc;
    
    return r;
}

// 生成胜选结果（包括完成选手的升级操作）
Result OnWin(Person const* p, std::string_view desc)
{
    std::cout << "\t" << p->GetNo() << " 号选手胜选\n";
    
    std::cout << "\n【升级】\n";   
    
    Beauty* beauty = new Beauty(*p);
    delete p; // 重要：释放海选选手身份
    
    return { false, beauty, std::string(desc)}; // 聚合初始化
}

// 生成胜选评价 （利用选手的编号，生成变化的评价）
std::string MakePraise(int no)
{
    int index = no % 5; // 求余，故为： 0~4
    
    if (index == 0) { return "天生丽质"; }
    if (index == 1) { return "貌若天仙"; }
    if (index == 2) { return "倾国倾城"; }
    if (index == 3) { return "国色天香"; }		
    
    return "秀外慧中";
}

// 海选检测函数（通过的选手将升级）
Result Check(Person const * p)
{
    std::cout << "\n【检测】\n";
    std::cout << p->GetNo() << " 号选手正在接受检测……\n";
    
    if (p->GetGender() != 0) { return OnLost(p, "不是女性"); }
    std::cout << "\t>性别合规\n";

    if (p->GetAge() < 18) { return OnLost(p, "未满十八"); }
    if (p->GetAge() > 38) { return OnLost(p, "年龄超标"); }
    std::cout << "\t>年龄合规\n"; 

    if (p->GetHeight() < 151){ return OnLost(p, "身高略逊"); }
    if (p->GetHeight() > 189) { return OnLost(p, "身高超标"); }
	std::cout << "\t>身高合规\n";

    if (p->GetWeight() < 35) { return OnLost(p, "体重过轻"); }
    if (p->GetWeight() > 85) {return OnLost(p, "过于丰盈"); }
	std::cout << "\t>体重合规\n";

    double m = p->GetHeight() / 100.0, bmi = p->GetWeight() / (m * m);
    
    if (bmi < 18.5) { return OnLost(p, "BMI指数过低"); }
    if (bmi > 24) { return OnLost(p, "BMI指数过高"); }
    std::cout << "\t>BMI达标\n";

    std::string desc = MakePraise(p->GetNo()); // 生成评价（客套话）
    return OnWin(p, desc);
}

// 打广告
void Advertising(std::string_view sponsor, std::string_view slogan)
{
    std::cout << "\n#*************#\n"
              << "\t" << slogan << "\n"
              << "\t" << sponsor << "（宣）\n"
              << "#*************#\n\n";
}

// 第一场（海选）
std::vector<Result> FirstRound()
{
    std::cout << "~~~~~~~~~~~~第2学堂网校选美大赛报名~~~~~~~~~~~~\n";
    
    std::vector<Result> results;
    
    while(true)
    {
        results.push_back(Check(SignUp()));
        std::cin.ignore(99, '\n');
        
        if (results.size() % 3 == 0)
        {
            Advertising("第2学堂", "让学习回归兴趣，让兴趣创造价值！");
        }

        std::cout << "\n继续录入？(y/n)：";

        char c;
        std::cin >> c;
        
        if (c != 'y' && c != 'Y')
        {
            break;
        }

        std::cin.ignore(99, '\n');
    }
    
    return results;
}

// 海选结果处理
std::vector<Beauty const*> HandOpenRoundResult (std::vector<Result> const &  results)
{
    std::cout << "~~~~~~~~~~~~第2学堂网校选美大赛报名~~~~~~~~~~~~\n";
    
    std::vector<Beauty const*> beauties;
    
    std::cout << "\n====海选结果公告====\n";
    std::cout << "报名人数：" << results.size() << "\n";
    
    int lostCount = 0;
    for (auto const& r : results)
    {
        if (r.lost)
        {
            ++lostCount;
        }
    }
    
    std::cout << "\t其中有 " << lostCount << " 名选手遗憾落选\n";
    std::cout << "下面有请各位选手上场并发表赛后感言！\n";
    std::cout << "====================================\n\n";
    
    for (auto const& r : results)
    {
        std::cout << "#" << r.contestant->GetNo() << "号选手感言：\n";
        
        r.contestant->Speech(r.desc);
        
        if (r.lost)
        {
            std::cout << "\t请给 " << r.contestant->GetNo() << " 号选手最后的掌声！\n";
            delete r.contestant;
        }
        else
        {
            std::cout << "\t有请 " << r.contestant->GetNo() << " 号选手落座胜选席！\n";
            beauties.push_back(dynamic_cast<Beauty const*> (r.contestant));
        }
        
        std::cout << std::endl;
    }
    
    std::cout << "====================================\n";

    if (!beauties.empty())
    {
        std::cout << "恭喜" << beauties.size() << "位选手进入决赛！\n";
    }
    else
    {
        std::cout << "遗憾！本次海选无一人入选！\n（麦克风隐约传来：来的都是什么歪瓜裂枣哪！）\n";
    }
    
    return beauties;
}

// 计算身高得分 (入选范围：[151, 189]，理想身高：170)
// 得分范围：[0, 80]
double calculateHeightScore(int height)
{
    // 海选过关条件
    if (height < 151 || height > 189)
    {
        return 0.0;
    }

    // 选美赛中国女性理想身高标准值, 取中国年轻女性平均身高：162cm + 8cm
    double const ideal = 170.0; // 理想身高（cm）
    double diff = height - ideal;

    if (diff<=0.0)
    {
       return 50.0 + diff * 2.6316; // 每低 1cm 约减 2.63分
    }
    else
    {
       return 80.0 - diff * 1.5789; // 每高 1cm 减约 1.58分
    }
}

// 计算胸围得分 (理想胸围: 身高*0.53)
// 得分范围：[0, 100]
double calculateBustScore(int bust, int height)
{
    double ideal = height * 0.53; // 理想胸围（cm）
    double diff = std::abs(bust-ideal); 

    if (diff > 15.0) // 相差太多不得分
    {
        return 0.0;
    } 

    return 100.0 - diff * (100.0/15.0); // 每超出1cm 减 6.67分
}

// 计算腰围得分 (理想腰围: 身高*0.37)
// 得分范围：[0, 100]
double calculateWaistScore(int waist, int height)
{
    double ideal = height * 0.37; // 理想腰围（cm）
    double diff = std::abs(waist-ideal);

    if (diff > 12.0) // 相差太多不得分
    {
        return 0.0;
    }
    
    return 100.0 - diff * (100.0/12.0); // 每超出1cm 减 8.33分
}

// 计算臀围得分 (理想臀围: 身高*0.542)
// 得分范围: [0, 100]
double calculateHipScore(int hip, int height) 
{
    double ideal = height * 0.542; // 理想臀围（cm）
    double diff = std::abs(hip-ideal);
    
    if (diff > 15.0)
    {
        return 0.0;
    } 
    
    return 100.0 - diff * (100.0/15.0);
}

// 腰臀比得分详情
struct WHRScore
{
    double value;   // 腰围 ÷ 臀围
    double score;   // 得分 [0, 90]
    std::string type; // 腰臀比类型描述
};

// 计算腰臀比得分 (理想腰臀比范围: 0.67-0.80) 
// 得分范围: [0, 90]
WHRScore calculateWHRScore(int waist, int hip) 
{
    assert(waist > 0 && hip > 0); 

    // 理想腰臀比范围
    double const ideal_min=0.67, ideal_max=0.70; 
    double whr = static_cast<double> (waist) / hip;

    // “楚宫腰”：太细，不健康，得分范围：[0, 40)
    if (whr < 0.60) 
    {
        return {whr, 40.0+(whr-0.60)*500.0, "楚宫腰"}; 
    }
    
    // “飞燕腰”：趋向健康，得分范围：[40, 90)
    if (whr < ideal_min) // 0.67
    {
        return {whr, 40.0+(whr-0.60)*500.0, "飞燕腰"}; 
    }
    
    // “沙漏腰”：黄金比例，健康、美丽，得分 90 分（本项满分）
    if (whr <= ideal_max) // 0.70
    {
        return {whr, 90.0, "沙漏腰"}; 
    }

    // “贵妃腰” ：仍然健康，但逐渐偏离理想值，得分范围: [60, 90)
    if (whr <= 0.80)
    {
        return {whr, 90.0-(whr-0.70)*(30.0/0.10), "贵妃腰"};
    }

    // “直筒腰”：腰臀比过大，健康风险增加，得分范围 ：[0, 60)
    return { 
        whr, 
        std::max(0.0, 60.0-(whr-0.80)*200.0), 
        "直筒腰"
    };
} // calculateWHRScore

// 计算BMI得分(入选范围: 18.5-24，理想指数：21.5）
// 得分范围：[0, 80]，二选实际可得分：[50, 80]
double calculateBMIScore(double bmi) 
{
    double const ideal = 21.5; // 理想BMI指数

    if (bmi<=16.0) return 0.0;  // 极低体重,不健康，不得分
    if (bmi<=18.5) return (bmi-16.0) * 20.0; // 流行的苗条: 	0→50分
    if (bmi<=ideal) return 50.0 + (bmi-18.5) * 10.0; // 健康上升，50→80分
    if (bmi<=24.0) return 80.0 - (bmi-ideal) * 12.0; // 健康下降，80→50分
    if (bmi<=27.0) return 50.0 - (bmi-24.0) * (20.0/3.0); // 过重 50→30分
    if (bmi<=30.0) return 30.0 - (bmi-27.0) * 5.0; // 肥胖: 30→15分

    return std::max(0.0, 15.0- (bmi-30.0) * 1.5); // 严重肥胖：15→0分 
}

// 决赛分数详情
struct FinalScore 
{
    double bmi; //BMI指数
    double bmiScore; //BMI得分
    double heightScore; //身高得分
    double bustScore,waistScore,hipScore; //三围得分
    double bwhScore; //三围综合得分
    WHRScore whrScore; //腰臀比得分

    double overallScore; //综合得分
};

// 计算决赛身材总分
FinalScore calculateFinalScore (Beauty const* b)
{
    FinalScore fs;
    
    int h = b->GetHeight();
    
    fs.bmi = b->GetWeight() / ((h/100.0) * (h/100.0)); 

    fs.bmiScore = calculateBMIScore(fs.bmi);
    fs.heightScore = calculateHeightScore(h);
    
    fs.bustScore = calculateBustScore(b->GetBust(), h);
    fs.waistScore = calculateWaistScore(b->GetWaist(), h);
    fs.hipScore = calculateHipScore(b->GetHip(), h);

    fs.whrScore = calculateWHRScore(b->GetWaist(), b->GetHip()); // 腰臀比
    
    // 三围综合得分
    fs.bwhScore = fs.bustScore * 0.4 + fs.waistScore * 0.3 + fs.hipScore * 0.3;

    // 最终得分
    fs.overallScore = fs.bmiScore * 0.14 + fs.heightScore * 0.08
                + fs.bwhScore * 0.62 + fs.whrScore.score * 0.16;
    
    return fs;
}

// 冠军
struct Champion
{
    Beauty const * beauty; //选手
    FinalScore const score; //成绩
    
    Champion(Beauty const * b, FinalScore const& s)
        : beauty(b), score(s)
    {}
};

// 二选（终赛），可能有多个并列第一
std::vector<Champion> FinalRound (std::vector<Beauty const*> const&  beauties)
{
    std::cout << "\n~~~~~~~~~~~~第2学堂选美决赛~~~~~~~~~~~~\n";
    
    std::vector<Champion> campions; 
    
    double overallScoreTop = 0.0;
    
    for (Beauty const* b : beauties)
    {
        // 当前选手得分
        FinalScore fs = calculateFinalScore(b);
        
        if (static_cast<int>(overallScoreTop * 100)  == static_cast<int>(fs.overallScore * 100))
        {
            campions.emplace_back(b, fs); // 就地构造
        }
        else if (fs.overallScore > overallScoreTop)
        {
            campions.clear();
            campions.emplace_back(b, fs); // 就地构造
                        
            overallScoreTop = fs.overallScore; // 重要哦！
        }
    }
    
    return campions;
}


// 公布指定冠军详情
void OuputChampion(Champion const& c)
{
    using std::cout;
    
    cout << "\t" << c.beauty->GetNo() << " 号选手！\n";
    cout << "\t" << c.beauty->GetName() << " ！\n";
    
    cout << "以下是她的得分详情：";
    
    cout << std::fixed << std::setprecision(2); // 避免显示成科学计算法，显示两位小数
    
    cout << "\n\t身高：" << c.beauty->GetHeight() << "厘米，得分：" 
        << c.score.heightScore;
                
    cout << "\n\t体重：" << c.beauty->GetWeight() << "公斤";
    cout << "\n\tBMI指数：" <<  c.score.bmi << "，得分：" << c.score.bmiScore; 
 
    cout << "\n\t三围数据：";
    cout << "\n\t胸围：" <<  c.beauty->GetBust() << ", 得分：" << c.score.bustScore;
    cout << "\n\t腰围：" <<  c.beauty->GetWaist() << ", 得分：" << c.score.waistScore;
    cout << "\n\t臀围：" <<  c.beauty->GetHip() << ", 得分：" << c.score.hipScore;
    cout << "\n\tWHR：" << c.score.whrScore.value 
        <<  " [" << c.score.whrScore.type << "]，得分：" << c.score.whrScore.score;
    cout << "\n\t---------------";
    cout << "\n\t综合得分：" << c.score.overallScore;
    cout << "\n--------------------------\n\n";
}

// 公布所有冠军详情
void OuputChampions(std::vector<Champion> const& champions)
{
    std::cout << "\n\n=============================\n\n"
            << "本次选美大奖得主";
    
    auto count = champions.size();
    
    if (count > 1)
    {
        std::cout << "共 " << count << " 位！她们是：\n";
    }
    else 
    {
        std::cout << "她是：\n";
    }
    
    for (auto const& champion : champions)
    {
        OuputChampion(champion);
    }
}

int main()
{
    auto results = FirstRound();
    
    Advertising("作者：南郁", 
            "语言语法是功，标准库三方库是武！\n\t练武不练功，到老一场空\n\t练功不练武，到老白辛苦\n"
            "\t学C++就用《白话C++》\n\t又练功来又练武！");
    
    auto beauties = HandOpenRoundResult(results);
    
    if (beauties.empty())
    {
        std::cout << "本次选美失败！" << std::endl;
        return -1;
    }       
        
    Advertising("d2school",  "只用浏览器，搞定 C++ 半壁江山！\n《C++ 快速感受与探索之旅》");

    auto champions = FinalRound(beauties);
    
    Advertising("www.d2school.com", "第2学堂——关学习，我们不制造焦虑");
    
    OuputChampions(champions);

    for (auto b : beauties) // 并不需要 auto* ，b 就是指针
    {
        delete b;
    }    
}

3. 测试数据

以下数据（身高、体重、三围）非真实，仅为方便程序员测试。

表格：测试数据

用你的程序，算出来，在笔记或作业里告诉我，谁是第一？