count()函数stl_std :: count（）函数以及C ++ STL中的示例

count()函数stl

C ++ STL std：count()函数 (C++ STL std:count() function)

The C++ STL contains the function std::count(), which is used to find the occurrence of the particular element in the given range. You can use this function with an array, string, vector, etc.

C ++ STL包含函数std :: count() ，该函数用于查找给定范围内特定元素的出现。您可以将此函数与数组，字符串，向量等一起使用。

To use this function, we have to use either <bits/stdc++> header or <algorithm> header.

要使用此功能，我们必须使用<bits / stdc ++>标头或<algorithm>标头。

Syntax of std::count() function:

std :: count()函数的语法：

    count( start_point , end_point , val/element);

Parameters:

参数：

start_point: from where we want to start searching or the initial position.
start_point：从我们要开始搜索的位置或初始位置。
end_ point: ending point till where you want to search the element or the final position.
end_ point：直到要搜索元素或最终位置的终点。
val/elements: value or the element to be searched.
val / elements：值或要搜索的元素。

Return value: It returns the numbers of occurrences of the element in the given range.

返回值：返回给定范围内元素的出现次数。

For example:

例如：

    If the given string is:
    str="Includehelpisthebesttechenicalcontentplace"

    Then if we count no of 'e's:
    i.e. 
    count(str.begin(), str.end(), 'e');
    
    Output: 8

Exceptions:

例外情况：

It throws exception when the element assignment is not proper or the iterator is out of range.
当元素分配不正确或迭代器超出范围时，它将引发异常。
In case of invalid parameters shows the undefined behaviors.
如果参数无效，则显示未定义的行为。

Time Complexity:

时间复杂度：

O(n) is the time complexity of the std::count() function as it follows searching.

O(n)是std :: count()函数在搜索之后的时间复杂度 。

Input Output format:

输入输出格式：

    Input:
    arr[] = { 3, 2, 1, 3, 3, 5, 3 };
    n = sizeof(arr) / sizeof(arr[0]);
    count(arr, arr + n, 3);

    Output:
    4

    Input:
    str = "includehelp"; 
    count(str.begin(), str.end(), 'e'); 

    Output:
    2

C ++程序演示std :: count()函数的示例 (C++ program to demonstrate example of std::count() function)

/*
	C++ program to count the number of occurences of
	particular element in array ,string, vector,etc.
*/

#include<bits/stdc++.h>
using namespace std;

int main()
{
	//declaration of integer array arr
	int arr[]={2,3,5,3,5,6,3,5,5,5,5,4,5,3,6,7};
	int s =sizeof(arr)/sizeof(arr[0]);

	//declaration of vector container n
	vector<int> n={1,2,3,4,2,2,2,5,5,3,2,2,2,7,2};

	// take a string str
	string str ="anagramandanagram";

	
	//Here, we search the count of 5 in the array arr
	//you may change it also 2,3,6 ...as wish
	cout << "Number of times 5 appears :";
	cout << count(arr, arr + s, 5);
	
	//Here, we search the count of 2 in the vector n
	//you may change it also 5,3,6... as wish
	cout << "\n\nNumber of times 2 appears : ";
	cout<<count(n.begin(), n.end(), 2);
	
	//Here, we search the count of 'a' in the string str
	//you may change it also b,c,d.. as wish	
	cout << "\n\nNumber of times 'a' appears : ";
	cout << count(str.begin(), str.end(), 'a');

	return 0;
}

Output

输出量

Number of times 5 appears :7 
 
Number of times 2 appears : 8
 
Number of times 'a' appears : 7

翻译自: https://www.includehelp.com/stl/std-count-function-with-example-in-cpp-stl.aspx

count()函数stl