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Number of subarrays consisting only of Pronic Numbers
  • Last Updated : 16 Apr, 2021

Given an array arr[] consisting of N positive integers, the task is to count the number of subarrays consisting only of pronic numbers.

Examples:

Input: arr[] = {5, 6, 12, 3, 4}
Output: 3
Explanation: The subarray that consists only of pronic numbers are: 

  1. {6}
  2. {12}
  3. {6, 12}

Therefore, the total count of such subarrays is 3.

Input: arr[] = {0, 4, 20, 30, 5}
Output:



Naive Approach: The simplest approach to solve the problem is to generate all possible subarrays of the given array and count those subarrays made up of pronic numbers only. After checking for all the subarrays, print the count obtained. 

Time Complexity: O(√M * N3), where M is the maximum element present in the array 
Auxiliary Space: O(N)

Efficient Approach: The above approach can be optimized by keeping the track of continuous sequences of pronic numbers and then, count the number of subarrays formed. 
Follow the steps below to solve the problem:

  • Initialize a variable, say count, to store the total count of subarrays, and a variable C, to store the count of continuous array elements which are pronic numbers.
  • Traverse the given array arr[] and perform the following steps:
    • If the current element arr[i] is a pronic number, then increment C by 1.
    • Otherwise, increment count by C * (C – 1)/2 to count the number of subarrays with C elements having pronic numbers and update C to 0.
  • Increment the value of count as C*(C – 1)/2.
  • After completing the above steps, print the value of count as the result.

Below is the implementation of the above approach:

C++




// C++ program for the approach
#include <iostream>
#include <cmath>
using namespace std;
 
// Function to check if a number
// is pronic number or not
bool isPronic(int n)
{
     
    // Iterate over the range [1, sqrt(N)]
    int range = sqrt(n);
     
    for(int i = 0; i < range + 1; i++)
    {
         
        // Return true if N is pronic
        if (i * (i + 1) == n)
            return true;    
    }
     
    // Otherwise, return false
    return false;
}
 
// Function to count the number of
// subarrays consisting of pronic numbers
int countSub(int *arr, int n)
{
     
    // Stores the count of subarrays
    int ans = 0;
     
    // Stores the number of consecutive
    // array elements which are pronic
    int ispro = 0;
     
    // Traverse the aray
    for(int i = 0; i < n; i++)
    {
         
        // If i is pronic
        if (isPronic(arr[i]))
            ispro += 1;
        else
            ispro = 0;
             
        ans += ispro;
    }
     
    // Return the total count
    return ans;
}
 
// Driver code
int main()
{
    int arr[5] = {5, 6, 12, 3, 4};
    int n = sizeof(arr) / sizeof(arr[0]);
     
    cout << countSub(arr, n);
     
    return 0;
}
 
// This code is contributed by rohitsingh07052

Java




// Java program for the approach
import java.lang.*;
class GFG
{
 
  // Function to check if a number
  // is pronic number or not
  static boolean isPronic(int n)
  {
 
    // Iterate over the range [1, sqrt(N)]
    int range = (int)Math.sqrt(n);
 
    for(int i = 0; i < range + 1; i++)
    {
 
      // Return true if N is pronic
      if (i * (i + 1) == n)
        return true;    
    }
 
    // Otherwise, return false
    return false;
  }
 
  // Function to count the number of
  // subarrays consisting of pronic numbers
  static int countSub(int[] arr, int n)
  {
 
    // Stores the count of subarrays
    int ans = 0;
 
    // Stores the number of consecutive
    // array elements which are pronic
    int ispro = 0;
 
    // Traverse the aray
    for(int i = 0; i < n; i++)
    {
 
      // If i is pronic
      if (isPronic(arr[i]))
        ispro += 1;
      else
        ispro = 0;
 
      ans += ispro;
    }
 
    // Return the total count
    return ans;
  }
 
  // Driver code
  public static void main(String[] args)
  {
    int[] arr = {5, 6, 12, 3, 4};
    int n = arr.length;
    System.out.print(countSub(arr, n));
  }
}
 
// This code is contributed by shivani

Python3




# Python3 program for the approach
 
# Function to check if a number
# is pronic number or not
def isPronic(n):
   
    # Iterate over the range [1, sqrt(N)]
    for i in range(int(n ** (1 / 2)) + 1):
       
        # Return true if N is pronic
        if i * (i + 1) == n:
            return True
           
    # Otherwise, return false
    return False
 
# Function to count the number of
# subarrays consisting of pronic numbers
def countSub(arr):
 
    # Stores the count of subarrays
    ans = 0
 
    # Stores the number of consecutive
    # array elements which are pronic
    ispro = 0
 
    # Traverse the aray
    for i in arr:
 
        # If i is pronic
        if isPronic(i):
            ispro += 1
        else:
            ispro = 0
 
        ans += ispro
         
    # Return the total count
    return ans
 
 
# Driver Code
 
arr = [5, 6, 12, 3, 4]
print(countSub(arr))

C#




// C# program for the approach
using System;
class GFG
{
 
  // Function to check if a number
  // is pronic number or not
  static bool isPronic(int n)
  {
 
    // Iterate over the range [1, sqrt(N)]
    int range = (int)Math.Sqrt(n);        
    for(int i = 0; i < range + 1; i++)
    {
 
      // Return true if N is pronic
      if (i * (i + 1) == n)
        return true;    
    }
 
    // Otherwise, return false
    return false;
  }
 
  // Function to count the number of
  // subarrays consisting of pronic numbers
  static int countSub(int[] arr, int n)
  {
 
    // Stores the count of subarrays
    int ans = 0;
 
    // Stores the number of consecutive
    // array elements which are pronic
    int ispro = 0;
 
    // Traverse the aray
    for(int i = 0; i < n; i++)
    {
 
      // If i is pronic
      if (isPronic(arr[i]))
        ispro += 1;
      else
        ispro = 0;
      ans += ispro;
    }
 
    // Return the total count
    return ans;
  }
 
  // Driver code
  static void Main() {
    int[] arr = {5, 6, 12, 3, 4};
    int n = arr.Length;
 
    Console.WriteLine(countSub(arr, n));
  }
}
 
// This code is contributed by divyesh072019.

Javascript




<script>
// Javascript program for the approach
 
// Function to check if a number
// is pronic number or not
function isPronic(n)
{
     
    // Iterate over the range [1, sqrt(N)]
    let range = Math.sqrt(n);
     
    for(let i = 0; i < range + 1; i++)
    {
         
        // Return true if N is pronic
        if (i * (i + 1) == n)
            return true;    
    }
     
    // Otherwise, return false
    return false;
}
 
// Function to count the number of
// subarrays consisting of pronic numbers
function countSub(arr, n)
{
     
    // Stores the count of subarrays
    let ans = 0;
     
    // Stores the number of consecutive
    // array elements which are pronic
    let ispro = 0;
     
    // Traverse the aray
    for(let i = 0; i < n; i++)
    {
         
        // If i is pronic
        if (isPronic(arr[i]))
            ispro += 1;
        else
            ispro = 0;
             
        ans += ispro;
    }
     
    // Return the total count
    return ans;
}
 
// Driver code
let arr = [5, 6, 12, 3, 4];
let n = arr.length;
 
document.write(countSub(arr, n));
 
// This code is contributed by souravmahato348.
</script>
Output
3

Time Complexity: O(N*sqrt(M)), where M is the maximum element present in the array.
Auxiliary Space: O(1)

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