programming-examples/c++/Combinational_Problems/C++ Program to Find the Number of occurrences of a given Number using Binary Search approach.cpp

/*
 * C++ Program to Find the Number of occurrences of a given Number using Binary Search approach
 */
#include<iostream>
#include<conio.h>
using namespace std;
int first(int arr[], int low, int high, int x, int n)
{
    if (high >= low)
        {
            int mid = (low + high) / 2;
            if (( mid == 0 || x > arr[mid - 1]) && arr[mid] == x)
                {
                    return mid;
                }
            else if (x > arr[mid])
                {
                    return first(arr, (mid + 1), high, x, n);
                }
            else
                {
                    return first(arr, low, (mid - 1), x, n);
                }
        }
    return -1;
}
int last(int arr[], int low, int high, int x, int n)
{
    if (high >= low)
        {
            int mid = (low + high) / 2;
            if (( mid == n - 1 || x < arr[mid + 1]) && arr[mid] == x )
                {
                    return mid;
                }
            else if (x < arr[mid])
                {
                    return last(arr, low, (mid - 1), x, n);
                }
            else
                {
                    return last(arr, (mid + 1), high, x, n);
                }
        }
    return -1;
}
int count(int arr[], int x, int n)
{
    int i;
    int j;
    i = first(arr, 0, n - 1, x, n);
    if (i == -1)
        {
            return i;
        }
    j = last(arr, i, n - 1, x, n);
    return j - i + 1;
}
int main()
{
    int n, i, x, arr[10];
    cout<<"enter the number of elements\n";
    cin>>n;
    for (i = 0; i < n; i++)
        {
            cout<<"enter element\n";
            cin>>arr[i];
        }
    cout<<"enter the element whose number of occurences to be found\n";
    cin>>x;
    int c = count(arr, x, n);
    cout<<x<<" occurs "<<c<<" times "<<endl;
    getch();
}

/*

enter the number of elements
8
enter element
1
enter element
2
enter element
2
enter element
4
enter element
6
enter element
7
enter element
7
enter element
7
enter the element whose number of occurences to be found
4
4 occurs 1 times