【C++STL】Algorithm库

Algorithm库

copy_if()

语法：copy_if(first, last, out, pred)

作用：按传入的对象pred条件复制容器内容

如实现查找string数组中指定单词

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template<typename T, typename P>
std::vector<T> Filter(const std::vector<T>& vec, P pred){
    std::vector<T> res;
    std::copy_if(vec.begin(),vec.end(),std::back_inserter(res),pred);
    return res;
}

int main(void){
    std::string word="apple";
    auto hasWord = [&word](const std::string& s) {return s. find(word) != s.npos;};
    std::vector<std::string> words{"An apple","big apple","orange","green apple","grape"};
    std::vector<std::string> res = Filter(words, hasWord);

    for(auto s:res)
    std::cout << s << " " << std::endl;
 
}

C++20中，在range库中进行了拓展

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int main(void){
    std::string word="apple";
    auto hasWord = [&word](const std::string& s) {return s. find(word) != s.npos;};
    std::vector<std::string> words{"An apple","big apple","orange","green apple","grape"};
    std::vector<std::string> res ;
    std::ranges::copy_if(words, std::back_inserter(res),hasWord);

    for(auto s:res)
    std::cout << s << " " << std::endl;
 
}

partition()

语法：copy_if(first, last, pred)

作用：将一个序列按条件分割

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int main(void)
{

    std::vector<int> numbers{1,23,4,5,67,8,67,23,20,11,32,33,45,17};
    auto bound1 = std::partition(numbers.begin(),numbers.end(), [](int v){return v%3 == 0;});
    auto bound2 = std::partition(bound1, numbers. end(), [](int v){return v%3 == 1;});
    std::cout << "\n{x=3k}:\n";
    std::for_each(numbers.begin(),bound1, [](int v){std::cout << v << "";});
    std::cout << "\n{x=3k+1}:\n";
    std::for_each(bound1,bound2, [](int v){std::cout << v << "";});
    std::cout << "\n{x=3k+2}:\n";
    std::for_each(bound2,numbers.end(), [](int v){std::cout << v << "";});
}

序列运算

• set_difference()：将不是两个序列共有的元素拷贝到单独的元素中（差集）
• set_symmetric_difference()：上述加了绝对值（对称差集）
• set_intersection()
• set_union()

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int main(void){

    std::vector<int> numbers1{1,1,2,3,4,4,5,6};
    std::vector<int> numbers2{9,8,7,6,5,5,4};
    std::vector<int> result;

    std::sort(numbers1.begin(),numbers1.end());
    std::sort(numbers2.begin(),numbers2.end());

    std::set_symmetric_difference(numbers1.begin(),numbers1.end(),
    numbers2.begin(),numbers2.end(),
    std::back_insert_iterator(result));

    for(auto v:result)
        std::cout << v << " ";	
   
}

序列操作

• for_each()
• transform()
• remove_if()
• reduce()
• inner_product()
• transform_reduce()
• transform_exclusive_scan()