Finding count of a number in a sorted array

In Competitive programming, learning to use the standard library than coding from scratch saves a lot of time. In this post we will use C++ STL(Standard Template Library) binary search algorithm with an example.
Given a sorted array of numbers, How to find the frequency of a given number?

Here is an efficient algorithm to do it. Use binary search to find the left-most(L), and right-most(R) occurrence of the given number. Then R-L+1 gives us the result. 

C++ STL has two functions namely lower_bound, upper_bound which finds out the left-most and right-most occurrences of a given number in a sorted array.
The lower_bound() function returns an iterator to the left-most element, and the upper_bound() function returns an iterator to one element beyond right-most occurrence. So the difference of these two gives the count.

Here is the C++ code.

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

int getCount(vector<int> & numVector, int d)
int result = 0;
vector<int>::iterator left, right;
//find the left-most occurence
left = lower_bound( numVector.begin(), numVector.end(), d );
//find right-most occurence only if the number is present
if( left != numVector.end() )
right = upper_bound( numVector.begin(), numVector.end(), d );
result = right-left; //right points to one element beyond.
return result;
int main()
int n;
//read array size
int i,num;
vector<int> nums;
//read the array
for( i = 0 ; i < n ; i++ )
//read the number to be counted
return 0;

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