C++ std::is_sorted_until用法及代碼示例

std::is_sorted_until用於查找範圍[first，last)中的第一個未排序元素。它將迭代器返回到範圍中的第一個未排序元素，因此在first和返回的迭代器之間的所有元素都進行了排序。

也可以用來計算總數。範圍內已排序元素的數量。它在頭文件中定義。如果整個範圍都已排序，它將返回一個指向last的迭代器。

可以按以下兩種方式使用它：

1. 使用“ <”比較元素：
   用法:

   template 
   ForwardIterator is_sorted_until (ForwardIterator first, ForwardIterator last);
   
   first: Forward iterator to the first element in the list.
   last: forward iterator to the last element in the list.
   
   返回值：It returns an iterator to the first 
   unsorted element in the list.
   It returns last in case if there is only one element in 
   the list or if all the elements are sorted.
   

   // C++ program to demonstrate the use of std::is_sorted_until 
   #include <iostream> 
   #include <algorithm> 
   using namespace std; 
   int main() 
   { 
       int v[] = { 1, 2, 3, 4, 7, 10, 8, 9 }, i; 
     
       int* ip; 
     
       // Using std::is_sorted_until 
       ip = std::is_sorted_until(v, v + 8); 
     
       cout << "There are " << (ip - v) << " sorted elements in "
            << "the list and the first unsorted element is " << *ip; 
     
       return 0; 
   }

   輸出：

   There are 6 sorted elements in the list and the first unsorted element is 8
   

2. 通過使用預定義函數進行比較：

   用法:

   template 
    ForwardIterator is_sorted_until (ForwardIterator first, ForwardIterator last,
                                     Compare comp);
   
   Here, first and last are the same as previous case.
   
   comp: Binary function that accepts two elements in the 
   range as arguments, and returns a value convertible to bool.
   The value returned indicates whether the element passed as
   first argument is considered to go before the second in the specific
   strict weak ordering it defines.
   
   The function shall not modify any of its arguments.
   This can either be a function pointer or a function object.
   
   返回值：It returns an iterator 
   to the first unsorted element in the list.
   It returns last in case if there is only one element in 
   the list or if all the elements are sorted.

   // C++ program to demonstrate the use of std::nth_element 
   // C++ program to demonstrate the use of std::nth_element 
   #include <iostream> 
   #include <algorithm> 
   using namespace std; 
     
   // Defining the BinaryFunction 
   bool comp(int a, int b) 
   { 
       return (a < b); 
   } 
   int main() 
   { 
       int v[] = { 1, 3, 20, 10, 45, 33, 56, 23, 47 }, i; 
       int* ip; 
     
       // Using std::is_sorted_until 
       ip = std::is_sorted_until(v, v + 9, comp); 
     
       cout << "There are " << (ip - v) << " sorted elements in "
            << "the list and the first unsorted element is " << *ip; 
     
       return 0; 
   }

   輸出：

   There are 3 sorted elements in the list and the first unsorted element is 10