# Maximum number of consecutive 1s after flipping all 0s in a K length subarray

Given a binary array arr[] of length N, and an integer K, the task is to find the maximum number of consecutive ones after flipping all zero in a subarray of length K.

Examples:

Input: arr[]= {0, 0, 1, 1, 1, 1, 0, 1, 1, 0}, K = 2
Output:
Explanation:
On taking the subarray [6, 7] and flip zero to one we get 7 consecutive ones.

Input: arr[]= {0, 0, 1, 1, 0, 0, 0, 0}, K = 3
Output:
Explanation:
On taking the subarray [4, 6] and flip zero to one we get 5 consecutive ones.

Approach: To solve the problem follow the steps given below:

• Initialize a variable let’s say trav which is going to iterate in the array from each position i  to (0 to i-1) in the left direction and from (i+k  to n-1) in the right direction.
• Check and keep an account that no zero comes in its way in any direction while iterating in the array.
• If there is a 0 then break out from the loop in that direction.
• So ultimately for i to i+k if there is any zero we are already flipping it to 1 so no need to count number of ones in this range as it will be equal to integer K only.

Below is the implementation of the above approach:

## C++

 `// CPP program for the above approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function to find the maximum number of ` `// consecutive 1's after flipping all ` `// zero in a K length subarray ` `int` `findmax(``int` `arr[], ``int` `n, ``int` `k) ` `{ ` `    ``// Initialize variable ` `    ``int` `trav, i; ` `    ``int` `c = 0, maximum = 0; ` ` `  `    ``// Iterate unil n-k+1 as we ` `    ``// have to go till i+k ` `    ``for` `(i = 0; i < n - k + 1; i++) { ` `        ``trav = i - 1; ` `        ``c = 0; ` ` `  `        ``/*Iterate in the array in left direction ` `        ``till you get 1 else break*/` `        ``while` `(trav >= 0 && arr[trav] == 1) { ` `            ``trav--; ` `            ``c++; ` `        ``} ` `        ``trav = i + k; ` ` `  `        ``/*Iterate in the array in right direction ` `        ``till you get 1 else break*/` `        ``while` `(trav < n && arr[trav] == 1) { ` `            ``trav++; ` `            ``c++; ` `        ``} ` `        ``c += k; ` ` `  `        ``// Compute the maximum length ` `        ``if` `(c > maximum) ` `            ``maximum = c; ` `    ``} ` ` `  `    ``// Return the length ` `    ``return` `maximum; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `k = 3; ` `    ``// Array initialization ` `    ``int` `arr[] = { 0, 0, 1, 1, 0, 0, 0, 0 }; ` ` `  `    ``// Size of array ` `    ``int` `n = ``sizeof` `arr / ``sizeof` `arr; ` `    ``int` `ans = findmax(arr, n, k); ` `    ``cout << ans << ``'\n'``; ` `}`

## Python3

 `# Python3 program for the above approach ` ` `  `# Function to find the maximum number of ` `# consecutive 1's after flipping all ` `# zero in a K length subarray ` `def` `findmax(arr, n, k): ` `     `  `    ``# Initialize variable ` `    ``trav, i ``=` `0``, ``0` `    ``c ``=` `0` `    ``maximum ``=` `0` ` `  `    ``# Iterate unil n-k+1 as we ` `    ``# have to go till i+k ` `    ``while` `i < n ``-` `k ``+` `1``: ` `        ``trav ``=` `i ``-` `1` `        ``c ``=` `0` ` `  `        ``# Iterate in the array in left direction ` `        ``# till you get 1 else break ` `        ``while` `trav >``=` `0` `and` `arr[trav] ``=``=` `1``: ` `            ``trav ``-``=` `1` `            ``c ``+``=` `1` `        ``trav ``=` `i ``+` `k ` ` `  `        ``# Iterate in the array in right direction ` `        ``# till you get 1 else break ` `        ``while` `(trav < n ``and` `arr[trav] ``=``=` `1``): ` `            ``trav ``+``=` `1` `            ``c ``+``=` `1` ` `  `        ``c ``+``=` `k ` ` `  `        ``# Compute the maximum length ` `        ``if` `(c > maximum): ` `            ``maximum ``=` `c ` `        ``i ``+``=` `1` ` `  `    ``# Return the length ` `    ``return` `maximum ` ` `  `# Driver code ` `if` `__name__ ``=``=` `'__main__'``: ` `    ``k ``=` `3` `     `  `    ``# Array initialization ` `    ``arr ``=` `[``0``, ``0``, ``1``, ``1``, ``0``, ``0``, ``0``, ``0``] ` ` `  `    ``# Size of array ` `    ``n ``=` `len``(arr) ` `    ``ans ``=` `findmax(arr, n, k) ` `    ``print``(ans) ` ` `  `# This code is contributed by Mohit Kumar `

Output:

```5
```

Time complexity: O(N)

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Improved By : mohit kumar 29