C++ std::is_sorted用法及代码示例

C++函数std::is_sorted检查范围[first，last]中的元素是否按升序排序。使用<运算符比较元素。 std::is_sorted有两种变体：

1. 不使用二元谓词

   bool is_sorted( ForwardIt first, ForwardIt last );
   first, last: the range of elements to examine
   返回值： 
   true: if the elements are in non-decreasing order.
   false: any element in increasing order.
   

   例：
   给定一个大小为n且范围在[0…n]之间的容器，编写一个程序来检查它是否按升序排序。数组中允许相等值，并且认为两个连续的相等值已排序。

   Input:2 5 9 4      /*Range = 3*/
   Output:Sorted in given range.
   
   Input:3 5 1 9     /*Range = 3*/
   Output:Not sorted in given range.
   

   // CPP program to illustrate 
   // std::is_sorted 
   // without binary predicate 
   #include <iostream> 
   #include <algorithm> 
     
   // Driver Code 
   int main() 
   { 
       int A[] = { 10, 11, 15, 12 }; 
     
       // Index 0 to 2 
       int range1 = 3; 
     
       // Index 0 to 3 
       int range2 = 4; 
     
       // Condition if container is sorted or not in range1 
       if (std::is_sorted(A, A + range1)) { 
           std::cout << "Sorted in the range:" << range1 << std::endl; 
       } else { 
           std::cout << "Not Sorted in the range:" << range1 << std::endl; 
       } 
     
       // Condition if container is sorted or not in range2 
       if (std::is_sorted(A, A + range2)) { 
           std::cout << "Sorted in the range:" << range2 << std::endl; 
       } else { 
           std::cout << "Not Sorted in the range:" << range2 << std::endl; 
       } 
       return 0; 
   }

   输出：

   
   

   Sorted in the range:3
   Not Sorted in the range:4
   

   我们在这里讨论了其他方法。

2. 使用二进制谓词

   bool is_sorted (ForwardIt first, ForwardIt last, Compare comp);
   first, last: the range of elements to examine
   comp: binary predicate
   返回值： 
   true: if the elements are in non-decreasing order.
   false: any element in increasing order.
   

   例：
   给定一个仅由字符组成的字符串。检查字符是否按顺序排列。另外，在比较时忽略案例，即“ f”>“ A”

   Input:AHZP
   Output:Not Sorted
   
   Input:Boy
   Output:Sorted
   

   // CPP program to illustrate 
   // std::is_sorted 
   // using binary predicate 
   #include <iostream> 
   #include <algorithm> 
     
   using namespace std; 
     
   // Binary predicate 
   bool ignore_case(char a, char b) 
   { 
       // Converts both characters to lowercase and checks if a <= b 
       return (tolower(a) <= tolower(b)); 
   } 
     
   // Function that checks if string is sorted while ignoring the case 
   bool check_if_sorted(string str) 
   { 
       // Function call to is_sorted with binary predicate ignore_case 
       return is_sorted(str.begin(), str.end(), ignore_case); 
   } 
     
   // Driver code 
   int main() 
   { 
       // String which is to be checked 
       string str = "tOY"; 
     
       // Function returned true, string is sorted 
       if (check_if_sorted(str)) { 
           cout << "Sorted"; 
       } 
       // Function returned false, string not sorted 
       else { 
           cout << "Not sorted"; 
       } 
     
       return 0; 
   }

   输出：

   Sorted