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Merge the elements in subarray of all even elements of the Array
  • Last Updated : 25 Sep, 2020

Given an array arr[] containing N numbers, the task is to merge the subarray of consecutive even numbers by replacing all consecutive even numbers by the first even element of that subarray.
Note: A series of even integers are said to be consecutive if there are at least three even numbers in the given series. Therefore, merge elements in subarray which have at least 3 consecutive even numbers.
Examples:

Input: arr[] = {2, 2, 2, 100, 5, 4, 2, 9, 10, 88, 24} 
Output: 2 5 4 2 9 10 
Explanation: 
The given series contains two consecutive even subsequences. They are: 
{2, 2, 2, 100}, {10, 88, 24}. The two subsequences have to be merged to the first element in the subseries. 
Therefore, {2, 2, 2, 100} is replaced by 2 and {10, 88, 24} is replaced by 10 in the original series.
Input: arr[] = {2, 4, 5, 3, 6, 8, 10, 3, 4} 
Output: 2 4 5 3 6 3 4

Approach: In order to solve this problem, we need to first find if there exists a consecutive even subsequence with a size greater than three. Therefore, the idea is to iterate through the given array and check if a number is even or not.

  • Traverse through the array.
  • Check if the element is even or not.
  • If it is even, creates a temporary array to store the next continuous even numbers until the next number is odd.
  • Continue adding the elements in the temp array until an odd number occurs.
  • If the size of this temporary array is greater than three, then remove these elements from the given array and replace them with the first element of this temporary array.
  • Empty the temporary array to compute the next set of even subsequences.

Below is the implementation of the above approach:

C++

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// C++ program to merge the array
// as per the given condition
#include<bits/stdc++.h>
using namespace std;
 
// Function to merge the array
// as per the given condition
vector<int> merge(vector<int> arr)
{
     
    // Variable to store the final
    // sequence
    vector<int> ans;
 
    // Temporary array to store the
    // even numbers while traversing
    vector<int> e;
    int i = 0;
    int j = 0;
    int count = 0;
     
    // Iterating through the array
    while(i < arr.size())
    {
         
        // If the element is even
        if(arr[i] % 2 == 0)
        {
            j = i;
             
            // Iterating till an odd element
            // is found
            while(j < arr.size())
            {
                 
                // Keep appending into the
                // temporary array if the
                // even number is occurred
                if (arr[j] % 2 == 0)
                {
                    e.push_back(arr[j]);
                    count += 1;
                }
 
                // Break if an odd number
                // has occurred
                else
                    break;
                 
                j += 1;
            }
     
            // If the series has at least
            // three elements, then merge
            if(count >= 3)
               ans.push_back(e[0]);
 
            // Else, add all elements to the
            // answer array
            else
            {
                for (auto i: e)
                     ans.push_back(i);
            }
                 
            // Reseting the count and
            // temp array
            count = 0;
            e.clear();
            i = j;
        }
             
        // If the element is odd, add
        // it to the answer array
        else
        {
            ans.push_back(arr[i]);
            i += 1;
        }
    }
     
    return ans;
}
         
// Driver code
int main()
{
 
    vector<int> arr({ 2, 2, 2, 100, 5, 4,
                      2, 9, 10, 88, 24 });
    vector<int> ans = merge(arr);
     
    cout << "[";
    for(int i= 0; i < ans.size(); i++)
    {
        if(i == ans.size() - 1)
        cout << ans[i] << "]";
        else
        cout << ans[i] << ", ";
    }
 
}
     
// This code is contributed by Samarth

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Java

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// Java program to merge the array
// as per the given condition
import java.util.*;
  
class GFG{
  
// Function to merge the array
// as per the given condition
static Vector<Integer> merge(int []arr)
{
      
    // Variable to store the final
    // sequence
    Vector<Integer> ans = new Vector<Integer>();
  
    // Temporary array to store the
    // even numbers while traversing
    Vector<Integer> e = new Vector<Integer>();
     
    int i = 0;
    int j = 0;
    int count = 0;
      
    // Iterating through the array
    while (i < arr.length)
    {
          
        // If the element is even
        if (arr[i] % 2 == 0)
        {
            j = i;
              
            // Iterating till an odd element
            // is found
            while (j < arr.length)
            {
                  
                // Keep appending into the
                // temporary array if the
                // even number is occurred
                if (arr[j] % 2 == 0)
                {
                    e.add(arr[j]);
                    count += 1;
                }
  
                // Break if an odd number
                // has occurred
                else
                    break;
                  
                j += 1;
            }
      
            // If the series has at least
            // three elements, then merge
            if (count >= 3)
               ans.add(e.get(0));
  
            // Else, add all elements to the
            // answer array
            else
            {
                for(int ii : e)
                     ans.add(ii);
            }
                  
            // Reseting the count and
            // temp array
            count = 0;
            e.clear();
            i = j;
        }
              
        // If the element is odd, add
        // it to the answer array
        else
        {
            ans.add(arr[i]);
            i += 1;
        }
    }
    return ans;
}
          
// Driver code
public static void main(String[] args)
{
  
    int []arr = { 2, 2, 2, 100, 5, 4,
                  2, 9, 10, 88, 24 };
                   
    Vector<Integer> ans = merge(arr);
      
    System.out.print("[");
    for(int i= 0; i < ans.size(); i++)
    {
        if (i == ans.size() - 1)
            System.out.print(ans.get(i) + "]");
        else
            System.out.print(ans.get(i) + ", ");
    }
}
}
 
// This code is contributed by Amit Katiyar

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Python3

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# Python3 program to merge the array
# as per the given condition
 
# Function to merge the array
# as per the given condition
def merge(arr):
     
    # Variable to store the final
    # sequence
    ans = []
 
    # Temporary array to store the
    # even numbers while traversing
    e =[]
    i = 0
    j = 0
    count = 0
     
    # Iterating through the array
    while i<len(arr):
     
        # If the element is even
        if(arr[i]% 2 == 0):
            j = i
             
            # Iterating till an odd element
            # is found
            while j<len(arr):
                 
                # Keep appending into the
                # temporary array if the
                # even number is occurred
                if arr[j]% 2 == 0:
                     
                    e.append(arr[j])
                    count+= 1
 
                # Break if an odd number
                # has occurred
                else:
                    break
                 
                j+= 1
     
            # If the series has at least
            # three elements, then merge
            if(count>= 3):
                ans.append(e[0])
 
            # Else, add all elements to the
            # answer array
            else:
                for i in e:
                    ans.append(i)
                 
            # Reseting the count and
            # temp array
            count = 0
            e =[]
            i = j
 
        # If the element is odd, add
        # it to the answer array
        else:
            ans.append(arr[i])
            i+= 1
             
    return ans
        
# Driver code
if __name__ == "__main__":
     
    arr = [2, 2, 2, 100, 5, 4, 2, 9, 10, 88, 24]
     
    print(merge(arr))

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C#

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// C# program to merge the array
// as per the given condition
using System;
using System.Collections.Generic;
class GFG{
  
// Function to merge the array
// as per the given condition
static List<int> merge(int []arr)
{
  // Variable to store the final
  // sequence
  List<int> ans = new List<int>();
 
  // Temporary array to store the
  // even numbers while traversing
  List<int> e = new List<int>();
 
  int i = 0;
  int j = 0;
  int count = 0;
 
  // Iterating through the array
  while (i < arr.Length)
  {
    // If the element is even
    if (arr[i] % 2 == 0)
    {
      j = i;
 
      // Iterating till an odd element
      // is found
      while (j < arr.Length)
      {
        // Keep appending into the
        // temporary array if the
        // even number is occurred
        if (arr[j] % 2 == 0)
        {
          e.Add(arr[j]);
          count += 1;
        }
 
        // Break if an odd number
        // has occurred
        else
          break;
 
        j += 1;
      }
 
      // If the series has at least
      // three elements, then merge
      if (count >= 3)
        ans.Add(e[0]);
 
      // Else, add all elements to the
      // answer array
      else
      {
        foreach(int ii in e)
          ans.Add(ii);
      }
 
      // Reseting the count and
      // temp array
      count = 0;
      e.Clear();
      i = j;
    }
 
    // If the element is odd, add
    // it to the answer array
    else
    {
      ans.Add(arr[i]);
      i += 1;
    }
  }
  return ans;
}
          
// Driver code
public static void Main(String[] args)
{
  int []arr = {2, 2, 2, 100, 5, 4,
               2, 9, 10, 88, 24};
 
  List<int> ans = merge(arr);
  Console.Write("[");
   
  for(int i= 0; i < ans.Count; i++)
  {
    if (i == ans.Count - 1)
      Console.Write(ans[i] + "]");
    else
      Console.Write(ans[i] + ", ");
  }
}
}
 
// This code is contributed by 29AjayKumar

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Output: 

[2, 5, 4, 2, 9, 10]



Time Complexity: O(N2), where N is the length of the array.

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