C++ std::vector count统计某个元素个数 是否存在某个值

Posted 2021-10-29 软件工程小施同学

        int nCount = std::count(strVec.begin(), strVec.end(), target);
        if (nCount > 0)
        {
            std::cout << "method2: find " << target << " exists." << std::endl;
        }

#include <iostream>
#include <vector>
#include <string>

// 为了便于示例，声明全局容器
std::vector<std::string> strVec;

void methods(const std::string& target)
{
    // 方法一：遍历容器，查找相等元素判断是否存在
    {
        for (const auto& item : strVec)
        {
            if (item == target)
            {
                std::cout << "method1: find " << target << " exists." << std::endl;
                break;
            }
        }
    }
    // 方法二：获取元素个数，通过个数判断是否存在
    {
        int nCount = std::count(strVec.begin(), strVec.end(), target);
        if (nCount > 0)
        {
            std::cout << "method2: find " << target << " exists." << std::endl;
        }
    }
    // 方法三：查询元素迭代器，通过迭代器有效性判断是否存在
    {
        auto iter = std::find(strVec.begin(), strVec.end(), target);
        if (iter != strVec.end())
        {
            std::cout << "method3: find " << target << " exists." << std::endl;
        }
    }
    // 方法四：查询相等元素的迭代器，通过迭代器有效性判断是否存在
    {
        auto iter = std::find_if(strVec.begin(), strVec.end(), [&](const std::string& item)->bool
            { return (item == target); });
        if (iter != strVec.end())
        {
            std::cout << "method4: find " << target << " exists." << std::endl;
        }
    }
}

int main()
{
    strVec = { "C", "C++", "Java", "Python", "Lua", "Sql" };
    // 场景1：查找Ruby
    std::cout << "Find Ruby" << std::endl;
    methods("Ruby");
    // 场景2：查找C++
    std::cout << "Find C++" << std::endl;
    methods("C++");

    system("pause");
    return 0;
}

// result
/*
Find Ruby
Find C++
method1: find C++ exists.
method2: find C++ exists.
method3: find C++ exists.
method4: find C++ exists.
*/

std::vector 判断vector容器中是否存在某元素 - kaizen - 博客园