# Find the longest sub-array having exactly k odd numbers in C++

Suppose we have one array with n elements. The problem is to find longest sub-array which has exactly k odd numbers. So if A = [2, 3, 4, 11, 4, 12, 7], and k = 1, then output will be 4, sub-array is [4, 11, 4, 12]

We can solve this using sliding window. The task is like below −

• Initialize max := 0, count := 0, and start := 0
• for i in range 0 to n – 1, do the following
• if arr[i] mod 2 is not 0, then increase count by 1
• while count > k and start <= i, do the following
• if arr[start] mod 2 is not 0, then decrease count by 1
• increase start by 1
• if count = k, then
• if max < (i – start + 1), then max := (i – start + 1)
• return the max

## Example

Live Demo

#include<iostream>
using namespace std;
int oddSubarrayMaxLength(int arr[], int n, int k) {
int max_len = 0, count = 0, start = 0;
for (int i = 0; i < n; i++) {
if (arr[i] % 2 != 0)
count++;
while (count > k && start <= i)
if (arr[start++] % 2 != 0)
count--;
if (count == k)
if (max_len < (i - start + 1))
max_len = i - start + 1;
}
return max_len;
}
int main() {
int arr[] = {2, 3, 4, 11, 4, 12, 7};
int n = sizeof(arr) / sizeof(arr);
int k = 1;
cout << "Maximum Length is: "<< oddSubarrayMaxLength(arr, n, k);
}

## Output

Maximum Length is: 4