Functional Programming

1. `std::ranges::all_of`、`std::ranges::any_of`、`std::ranges::none_of`

template <class InputIterator, class UnaryPredicate>bool all_of (InputIterator first, InputIterator last, UnaryPredicate pred);template <class InputIterator, class UnaryPredicate>bool any_of (InputIterator first, InputIterator last, UnaryPredicate pred);template <class InputIterator, class UnaryPredicate>bool none_of (InputIterator first, InputIterator last, UnaryPredicate pred);

#include <iostream>
#include <vector>
#include <algorithm>int main() {std::vector<int> vec1{ 2,4,6,8,10 };std::vector<int> vec2{ 2,3,5,7,11,13,14,21,28,35 };/* 判断容器中是不是所有的元素都满足要求 */bool flag1 = std::all_of(vec1.cbegin(), vec1.cend(), [](int val) {if (val % 2 == 0) {return true;}else {return false;}});if (flag1){std::cout << "All numbers are even.\n";}/* 判断容器中是否有（至少一个）元素满足要求 */bool flag2 = std::any_of(vec2.cbegin(), vec2.cend(), [](int val) {if (val % 5 == 0) {return true;}else {return false;}});if (flag2){std::cout << "At least one number is divisible by 5.\n";}/* 判断容器中是不是所有元素都不满足要求 */bool flag3 = std::none_of(vec2.cbegin(), vec2.cend(), [](int val) {if (val >= 100) {return true;}else {return false;}});if (flag3){std::cout << "All numbers are less than 100.\n";}
}

2. `std::iota`

template <class ForwardIterator, class T>void iota (ForwardIterator first, ForwardIterator last, T val);

从初始值val开始递增1填充迭代器first和last（不含）之间的元素。

2.1 基础类型示例

#include <iostream>
#include <vector>
#include <numeric>     // std::iotaauto main()->void {std::vector<int> vec1(20);std::iota(vec1.begin(), vec1.end(), 3);for (const auto&it: vec1){std::cout << it << " ";  // 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22}std::cout << std::endl;
}

2.2 自定义类型示例

#include <iostream>
#include <vector>
#include <numeric>     // std::iota
#include <algorithm>   // std::for_each
#include <functional>  // std::mem_fn
#include <random>template<class T>
struct Increase
{void operator()() {val_ += static_cast<T>(1);}T val_;/* std::iota会用到 */Increase& operator=(T i) { val_ = i; return *this; }
};auto main()->void {std::vector<Increase<int>> vec1(20);std::iota(vec1.begin(), vec1.end(), 0);for (const auto&it: vec1){std::cout << it.val_ << " ";    // 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19}std::cout << std::endl;std::for_each(vec1.begin(), vec1.end(), std::mem_fn(&Increase<int>::operator()));//std::shuffle(vec1.begin(), vec1.end(), std::mt19937{ std::random_device{}() });for (const auto& it : vec1){std::cout << it.val_ << " ";    // 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20}std::cout << std::endl;
}