最小/最大操作(Minimum/maximum operations)

一、max

1、原型：

template< class T >
const T& max( const T& a, const T& b );template< class T, class Compare >
const T& max( const T& a, const T& b, Compare comp );template< class T >
T max( std::initializer_list<T> ilist );template< class T, class Compare >
T max( std::initializer_list<T> ilist, Compare comp );

2、说明：

返回a、b中较大的一个；返回ilist中最大一个。
std::initializer_list 和 vector 类似，不同的是，initializer_list对象中的元素永远是常量值，我们无法改变initializer_list对象中元素的值。

3、官方demo

#include <algorithm>
#include <iostream>
#include <string>int main()
{std::cout << "larger of 1 and 9999: " << std::max(1, 9999) << '\n'<< "larger of 'a', and 'b': " << std::max('a', 'b') << '\n'<< "longest of \"foo\", \"bar\", and \"hello\": " <<std::max( { "foo", "bar", "hello" },[](const std::string& s1, const std::string& s2) {return s1.size() < s2.size();}) << '\n';
}

Output:

larger of 1 and 9999: 9999
larger of 'a', and 'b': b
longest of "foo", "bar", and "hello": hello

二、max_element

1、原型：

template< class ForwardIt >
ForwardIt max_element( ForwardIt first, ForwardIt last );template< class ForwardIt, class Compare >
ForwardIt max_element( ForwardIt first, ForwardIt last, Compare comp );

2、说明：

返回[first, last)中最大的元素的位置（迭代器）

3、官方demo

#include <algorithm>
#include <iostream>
#include <vector>
#include <cmath>static bool abs_compare(int a, int b)
{return (std::abs(a) < std::abs(b));
}int main()
{std::vector<int> v{ 3, 1, -14, 1, 5, 9 }; std::vector<int>::iterator result;result = std::max_element(v.begin(), v.end());std::cout << "max element at: " << std::distance(v.begin(), result) << '\n';result = std::max_element(v.begin(), v.end(), abs_compare);std::cout << "max element (absolute) at: " << std::distance(v.begin(), result);
}

Output:

max element at: 5
max element (absolute) at: 2

三、min

1、原型：

template< class T >
const T& min( const T& a, const T& b );template< class T, class Compare >
const T& min( const T& a, const T& b, Compare comp );template< class T >
T min( std::initializer_list<T> ilist );template< class T, class Compare >
T min( std::initializer_list<T> ilist, Compare comp );

2、说明：

返回a、b中较小的一个；返回ilist中最小一个。

3、官方demo

#include <algorithm>
#include <iostream>
#include <string>int main()
{std::cout << "smaller of 1 and 9999: " << std::min(1, 9999) << '\n'<< "smaller of 'a', and 'b': " << std::min('a', 'b') << '\n'<< "shortest of \"foo\", \"bar\", and \"hello\": " <<std::min( { "foo", "bar", "hello" },[](const std::string& s1, const std::string& s2) {return s1.size() < s2.size();}) << '\n';
}

Output:

smaller of 1 and 9999: 1
smaller of 'a', and 'b': a
shortest of "foo", "bar", and "hello": foo

四、min_element

1、原型：

template< class ForwardIt >
ForwardIt min_element( ForwardIt first, ForwardIt last );template< class ForwardIt, class Compare >
ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );

2、说明：

返回[first, last)范围内，最小元素的位置（迭代器）

3、官方demo

#include <algorithm>
#include <iostream>
#include <vector>int main()
{std::vector<int> v{3, 1, 4, 1, 5, 9};std::vector<int>::iterator result = std::min_element(v.begin(), v.end());std::cout << "min element at: " << std::distance(v.begin(), result);
}

Output:

min element at: 1

五、minmax

1、原型：

template< class T >
std::pair<const T&,const T&> minmax( const T& a, const T& b );template< class T, class Compare >
std::pair<const T&,const T&> minmax( const T& a, const T& b, Compare comp );template< class T >
std::pair<T,T> minmax( std::initializer_list<T> ilist);template< class T, class Compare >
std::pair<T,T> minmax( std::initializer_list<T> ilist, Compare comp );

2、说明：

以std::pair成对返回最小、最大值。

3、官方demo

#include <algorithm>
#include <iostream>
#include <vector>
#include <cstdlib>
#include <ctime>int main()
{std::vector<int> v {3, 1, 4, 1, 5, 9, 2, 6}; std::srand(std::time(0));std::pair<int, int> bounds = std::minmax(std::rand() % v.size(),std::rand() % v.size());std::cout << "v[" << bounds.first << "," << bounds.second << "]: ";for (int i = bounds.first; i < bounds.second; ++i) {std::cout << v[i] << ' ';}std::cout << '\n';
}

Possible output:

v[2,7]: 4 1 5 9 2

六、minmax_element

1、原型：

template< class ForwardIt >
std::pair<ForwardIt,ForwardIt>minmax_element( ForwardIt first, ForwardIt last );template< class ForwardIt, class Compare >
std::pair<ForwardIt,ForwardIt>minmax_element( ForwardIt first, ForwardIt last, Compare comp );

2、说明：

成对（std::pair）返回[first, last)范围内最小、最大值的位置（迭代器）

3、官方demo

#include <algorithm>
#include <iostream>
#include <vector>int main() {const auto v = { 3, 9, 1, 4, 2, 5, 9 };const auto [min, max] = std::minmax_element(begin(v), end(v));std::cout << "min = " << *min << ", max = " << *max << '\n';
}

Output:

min = 1, max = 9

七、clamp 从C++17开始

1、原型：

template<class T>
constexpr const T& clamp( const T& v, const T& lo, const T& hi );template<class T, class Compare>
constexpr const T& clamp( const T& v, const T& lo, const T& hi, Compare comp );

2、说明：

如果v小于lo，返回lo；如果v大于hi，返回hi；否则返回v；即确保返回的值在lo和hi之间。

3、官方demo

#include <cstdint>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <random>int main()
{std::mt19937 g(std::random_device{}());std::uniform_int_distribution<> d(-300, 300);std::cout << " raw   clamped to int8_t   clamped to uint8_t\n";for(int n = 0; n < 5; ++n) {int v = d(g);std::cout << std::setw(4) << v<< std::setw(20) << std::clamp(v, INT8_MIN, INT8_MAX)<< std::setw(21) << std::clamp(v, 0, UINT8_MAX) << '\n';}
}

Possible output:

.raw   clamped to int8_t   clamped to uint8_t
168                 127                  168
128                 127                  128
-137                -128                 040                  40                  40-66                 -66                 0

比较运算（Comparison operations）

一、equal

1、原型：

template< class InputIt1, class InputIt2 >
bool equal( InputIt1 first1, InputIt1 last1, InputIt2 first2 );template< class InputIt1, class InputIt2, class BinaryPredicate >
bool equal( InputIt1 first1, InputIt1 last1, InputIt2 first2, BinaryPredicate p );

2、说明：

判读两个序列是否相同。

3、官方demo

#include <algorithm>
#include <iostream>
#include <string>// 判读是否是回文序列
bool is_palindrome(const std::string& s)
{return std::equal(s.begin(), s.begin() + s.size()/2, s.rbegin());
}void test(const std::string& s)
{std::cout << "\"" << s << "\" "<< (is_palindrome(s) ? "is" : "is not")<< " a palindrome\n";
}int main()
{test("radar");test("hello");
}

Output:

"radar" is a palindrome
"hello" is not a palindrome

二、lexicographical_compare

1、原型：

template< class InputIt1, class InputIt2 >
bool lexicographical_compare( InputIt1 first1, InputIt1 last1,InputIt2 first2, InputIt2 last2 );template< class InputIt1, class InputIt2, class Compare >
bool lexicographical_compare( InputIt1 first1, InputIt1 last1,InputIt2 first2, InputIt2 last2,Compare comp );

2、说明：

按照字典顺序比较第一个序列是否小于第二个序列。

3、官方demo

#include <algorithm>
#include <iostream>
#include <vector>
#include <random>int main()
{std::vector<char> v1 {'a', 'b', 'c', 'd'};std::vector<char> v2 {'a', 'b', 'c', 'd'};std::mt19937 g{std::random_device{}()};while (!std::lexicographical_compare(v1.begin(), v1.end(),v2.begin(), v2.end())) {for (auto c : v1) std::cout << c << ' ';std::cout << ">= ";for (auto c : v2) std::cout << c << ' ';std::cout << '\n';std::shuffle(v1.begin(), v1.end(), g);std::shuffle(v2.begin(), v2.end(), g);}for (auto c : v1) std::cout << c << ' ';std::cout << "< ";for (auto c : v2) std::cout << c << ' ';std::cout << '\n';
}

Possible output:

a b c d >= a b c d 
d a b c >= c b d a 
b d a c >= a d c b 
a c d b < c d a b