Find the number of elements greater than k in a sorted array

Given a sorted array arr[] of integers and an integer k, the task is to find the count of elements in the array which are greater than k. Note that k may or may not be present in the array.

Examples:

Input: arr[] = {2, 3, 5, 6, 6, 9}, k = 6
Output: 1

Input: arr[] = {1, 1, 2, 5, 5, 7}, k = 8
Output: 0



Approach: The idea is to perform binary search and find the number of elements greater than k.

Below is the implementation of the above approach:

C++

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// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to return the count of elements
// from the array which are greater than k
int countGreater(int arr[], int n, int k)
{
    int l = 0;
    int r = n - 1;
  
    // Stores the index of the left most element
    // from the array which is greater than k
    int leftGreater = n;
  
    // Finds number of elements greater than k
    while (l <= r) {
        int m = l + (r - l) / 2;
  
        // If mid element is greater than
        // k update leftGreater and r
        if (arr[m] > k) {
            leftGreater = m;
            r = m - 1;
        }
  
        // If mid element is less than
        // or equal to k update l
        else
            l = m + 1;
    }
  
    // Return the count of elements greater than k
    return (n - leftGreater);
}
  
// Driver code
int main()
{
    int arr[] = { 3, 3, 4, 7, 7, 7, 11, 13, 13 };
    int n = sizeof(arr) / sizeof(arr[0]);
  
    int k = 7;
  
    cout << countGreater(arr, n, k);
  
    return 0;
}

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Java

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// Java implementation of the approach
class GFG
{
      
// Function to return the count of elements
// from the array which are greater than k
static int countGreater(int arr[], int n, int k)
{
    int l = 0;
    int r = n - 1;
  
    // Stores the index of the left most element
    // from the array which is greater than k
    int leftGreater = n;
  
    // Finds number of elements greater than k
    while (l <= r) {
        int m = l + (r - l) / 2;
  
        // If mid element is greater than
        // k update leftGreater and r
        if (arr[m] > k) {
            leftGreater = m;
            r = m - 1;
        }
  
        // If mid element is less than
        // or equal to k update l
        else
            l = m + 1;
    }
  
    // Return the count of elements greater than k
    return (n - leftGreater);
}
  
// Driver code
public static void main(String[] args)
{
    int arr[] = { 3, 3, 4, 7, 7, 7, 11, 13, 13 };
    int n = arr.length;
  
    int k = 7;
  
    System.out.println(countGreater(arr, n, k));
}
}
  
// This code is contributed by Code_Mech

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Python3

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# Python 3 implementation of the approach
  
# Function to return the count of elements
# from the array which are greater than k
def countGreater(arr, n, k):
    l = 0
    r = n - 1
  
    # Stores the index of the left most element
    # from the array which is greater than k
    leftGreater = n
  
    # Finds number of elements greater than k
    while (l <= r):
        m = int(l + (r - l) / 2)
  
        # If mid element is greater than
        # k update leftGreater and r
        if (arr[m] > k):
            leftGreater = m
            r = m - 1
  
        # If mid element is less than
        # or equal to k update l
        else:
            l = m + 1
  
    # Return the count of elements 
    # greater than k
    return (n - leftGreater)
  
# Driver code
if __name__ == '__main__':
    arr = [3, 3, 4, 7, 7, 7, 11, 13, 13]
    n = len(arr)
    k = 7
  
    print(countGreater(arr, n, k))
# This code is contributed by
# Surendra_Gangwar

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C#

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// C# implementation of the approach
using System;
  
class GFG
{
      
// Function to return the count of elements
// from the array which are greater than k
static int countGreater(int[]arr, int n, int k)
{
    int l = 0;
    int r = n - 1;
  
    // Stores the index of the left most element
    // from the array which is greater than k
    int leftGreater = n;
  
    // Finds number of elements greater than k
    while (l <= r) 
    {
        int m = l + (r - l) / 2;
  
        // If mid element is greater than
        // k update leftGreater and r
        if (arr[m] > k) 
        {
            leftGreater = m;
            r = m - 1;
        }
  
        // If mid element is less than
        // or equal to k update l
        else
            l = m + 1;
    }
  
    // Return the count of elements greater than k
    return (n - leftGreater);
}
  
// Driver code
public static void Main()
{
    int[] arr = { 3, 3, 4, 7, 7, 7, 11, 13, 13 };
    int n = arr.Length;
  
    int k = 7;
  
    Console.WriteLine(countGreater(arr, n, k));
}
}
  
// This code is contributed by Code_Mech

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PHP

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<?php
// PHP implementation of the approach
  
// Function to return the count of elements
// from the array which are greater than k
function countGreater($arr, $n, $k)
{
    $l = 0;
    $r = $n - 1;
  
    // Stores the index of the left most element
    // from the array which is greater than k
    $leftGreater = $n;
  
    // Finds number of elements greater than k
    while ($l <= $r
    {
        $m = $l + (int)(($r - $l) / 2);
  
        // If mid element is greater than
        // k update leftGreater and r
        if ($arr[$m] > $k
        {
            $leftGreater = $m;
            $r = $m - 1;
        }
  
        // If mid element is less than
        // or equal to k update l
        else
            $l = $m + 1;
    }
  
    // Return the count of elements greater than k
    return ($n - $leftGreater);
}
  
// Driver code
$arr = array(3, 3, 4, 7, 7, 7, 11, 13, 13);
$n = sizeof($arr);
$k = 7;
  
echo countGreater($arr, $n, $k);
  
// This code is contributed
// by Akanksha Rai

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Output:

3

Time Complexity: O(log(n)) where n is the number of elements in the array.



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