Find the longest sub-array having exactly k odd numbers

Given an array of size n. The problem is to find the longest sub-array having exactly k odd numbers.

Examples:

Input : arr[] = {2, 3, 4, 11, 4, 12, 7}, k = 1
Output : 4
The sub-array is {4, 11, 4, 12}.

Input : arr[] = {3, 4, 6, 1, 9, 8, 2, 10}, k = 2
Output : 7
The sub-array is {4, 6, 1, 9, 8, 2, 10}.



Naive Approach: Consider all the sub-arrays and count the number of odd numbers in them. Return the length of the one having exactly ‘k’ odd numbers and has the maximum length. Time Complexity is of O(n^2).

Efficient Approach: The idea is to use sliding window.

longSubarrWithKOddNum(arr, n, k)
    Initialize max = 0, count = 0, start = 0

    for i = 0 to n-1
        if arr[i] % 2 != 0, then
        count++
    while (count > k && start <= i)    
        if arr[start++] % 2 != 0, then
            count--
    if count == k, then
        if max < (i - start + 1), then
            max = i - start + 1    
    return max

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ implementation to find the longest
// sub-array having exactly k odd numbers
#include <bits/stdc++.h>
using namespace std;
  
// function to find the longest sub-array
// having exactly k odd numbers
int longSubarrWithKOddNum(int arr[], int n, 
                                     int k)
{
    int max = 0, count = 0, start = 0;
      
    // traverse the given array
    for (int i = 0; i < n; i++) {
        // if number is odd increment count
        if (arr[i] % 2 != 0)
            count++;
          
        // remove elements from sub-array from 
        // 'start' index when count > k
        while (count > k && start <= i)    
            if (arr[start++] % 2 != 0)
                count--;
          
        // if count == k, then compare max with 
        // current sub-array length
        if (count == k)
            if (max < (i - start + 1))
                max = i - start + 1;
    }
      
    // required length
    return max;
}
  
// Driver program to test above
int main()
{
    int arr[] = {3, 4, 6, 1, 9, 8, 2, 10};
    int n = sizeof(arr) / sizeof(arr[0]);
    int k = 2;
      
    cout << "Length = "
         << longSubarrWithKOddNum(arr, n, k);
           
    return 0;     

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java implementation to find the longest
// sub-array having exactly k odd numbers
import java.io.*;
  
class GFG {
      
    // function to find the longest sub-array
    // having exactly k odd numbers
    static int longSubarrWithKOddNum(int arr[], int n, 
                                        int k)
    {
        int max = 0, count = 0, start = 0;
          
        // traverse the given array
        for (int i = 0; i < n; i++) 
        {
            // if number is odd increment count
            if (arr[i] % 2 != 0)
                count++;
              
            // remove elements from sub-array from 
            // 'start' index when count > k
            while (count > k && start <= i) 
                if (arr[start++] % 2 != 0)
                    count--;
              
            // if count == k, then compare max 
            // with current sub-array length
            if (count == k)
                if (max < (i - start + 1))
                    max = i - start + 1;
        }
          
        // required length
        return max;
    }
  
    // Driver program
    public static void main(String args[])
    {
        int arr[] = {3, 4, 6, 1, 9, 8, 2, 10};
        int n = arr.length;
        int k = 2;
      
        System.out.println("Length = " 
                          + longSubarrWithKOddNum(arr, n, k));
    }
}
  
  
// This code is contributed 
// by Nikita Tiwari.

chevron_right


Python3

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python3 implementation to find the longest
# sub-array having exactly k odd numbers
  
# Function to find the longest sub-array
# having exactly k odd numbers
def longSubarrWithKOddNum(arr, n, k) :
      
    mx, count, start = 0, 0, 0
  
    # Traverse the given array
    for i in range(0, n) :
          
        # if number is odd increment count
        if (arr[i] % 2 != 0) :
            count = count + 1
              
        # remove elements from sub-array from 
        # 'start' index when count > k
        while (count > k and start <= i) :
              
            if (arr[start] % 2 != 0) :
                count = count - 1
                  
            start = start + 1
          
        # if count == k, then compare max  
        # with current sub-array length
        if (count == k) :
            if (mx < (i - start + 1)) :
                mx = i - start + 1
      
    # required length
    return mx
      
  
# Driver Code
arr = [3, 4, 6, 1, 9, 8, 2, 10]
n = len(arr)
k = 2
  
print("Length = ", longSubarrWithKOddNum(arr, n, k))
  
# This code is contributed by Nikita Tiwari.

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# implementation to find the longest
// sub-array having exactly k odd numbers
using System;
  
class GFG {
      
    // function to find the longest sub-array
    // having exactly k odd numbers
    static int longSubarrWithKOddNum(int []arr, int n, 
                                                int k)
    {
        int max = 0, count = 0, start = 0;
          
        // traverse the given array
        for (int i = 0; i < n; i++) 
        {
            // if number is odd increment count
            if (arr[i] % 2 != 0)
                count++;
              
            // remove elements from sub-array from 
            // 'start' index when count > k
            while (count > k && start <= i) 
                if (arr[start++] % 2 != 0)
                    count--;
              
            // if count == k, then compare max 
            // with current sub-array length
            if (count == k)
                if (max < (i - start + 1))
                    max = i - start + 1;
        }
          
        // required length
        return max;
    }
  
    // Driver program
    public static void Main()
    {
        int []arr = {3, 4, 6, 1, 9, 8, 2, 10};
        int n = arr.Length;
        int k = 2;
      
        Console.WriteLine("Length = "
                        + longSubarrWithKOddNum(arr, n, k));
    }
}
  
  
// This code is contributed 
// by vt_m.

chevron_right


PHP

filter_none

edit
close

play_arrow

link
brightness_4
code

<?php
// PHP implementation to find the longest
// sub-array having exactly k odd numbers
  
// function to find the longest sub-array
// having exactly k odd numbers
function longSubarrWithKOddNum($arr, $n
                                    $k)
{
    $max = 0; $count = 0; $start = 0;
      
    // traverse the given array
    for ($i = 0; $i < $n; $i++)
    {
          
        // if number is odd increment count
        if ($arr[$i] % 2 != 0)
            $count++;
          
        // remove elements from sub-array from 
        // 'start' index when count > k
        while ($count > $k && $start <= $i
            if ($arr[$start++] % 2 != 0)
                $count--;
          
        // if count == k, then compare max with 
        // current sub-array length
        if ($count == $k)
            if ($max < ($i - $start + 1))
                $max = $i - $start + 1;
    }
      
    // required length
    return $max;
}
  
// Driver Code
{
    $arr = array(3, 4, 6, 1, 9, 8, 2, 10);
    $n = sizeof($arr) / sizeof($arr[0]);
    $k = 2;
      
    echo "Length = ", longSubarrWithKOddNum($arr, $n, $k);
    return 0;     
  
// This code is contributed by nitin mittal.
?>

chevron_right



Output :

Length = 7

Time Complexity: O(n).



My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.



Improved By : nitin mittal



Article Tags :
Practice Tags :


Be the First to upvote.


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.