# Maximum length L such that the sum of all subarrays of length L is less than K

Last Updated : 22 Jun, 2022

Given an array of length N and an integer K. The task is to find the maximum length L such that all the subarrays of length L have sum of its elements less than K.
Examples:

Input: arr[] = {1, 2, 3, 4, 5}, K = 20
Output:
The only subarray of length 5 is the complete
array and (1 + 2 + 3 + 4 + 5) = 15 < 20.

Input: arr[] = {1, 2, 3, 4, 5}, K = 10
Output:

Approach: For the maximum sum of a subarray of length K, go through the approach discussed in this article. Now, a binary search can be performed to find the maximum length. As the array elements are positive then increasing the subarray length will increase the maximum sum of the subarray elements for that length.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach` `#include ` `using` `namespace` `std;`   `// Function to return the maximum sum` `// in a subarray of size k` `int` `maxSum(``int` `arr[], ``int` `n, ``int` `k)` `{` `    ``// k must be greater` `    ``if` `(n < k) {` `        ``return` `-1;` `    ``}`   `    ``// Compute sum of first window of size k` `    ``int` `res = 0;` `    ``for` `(``int` `i = 0; i < k; i++)` `        ``res += arr[i];`   `    ``// Compute sums of remaining windows by` `    ``// removing first element of previous` `    ``// window and adding last element of` `    ``// current window.` `    ``int` `curr_sum = res;` `    ``for` `(``int` `i = k; i < n; i++) {` `        ``curr_sum += arr[i] - arr[i - k];` `        ``res = max(res, curr_sum);` `    ``}`   `    ``return` `res;` `}`   `// Function to return the length of subarray` `// Sum of all the subarray of this` `// length is less than or equal to K` `int` `solve(``int` `arr[], ``int` `n, ``int` `k)` `{` `    ``int` `max_len = 0, l = 0, r = n, m;`   `    ``// Binary search from l to r as all the` `    ``// array elements are positive so that` `    ``// the maximum subarray sum is monotonically` `    ``// increasing` `    ``while` `(l <= r) {` `        ``m = (l + r) / 2;`   `        ``// Check if the subarray sum is` `        ``// greater than K or not` `        ``if` `(maxSum(arr, n, m) > k)` `            ``r = m - 1;` `        ``else` `{` `            ``l = m + 1;`   `            ``// Update the maximum length` `            ``max_len = m;` `        ``}` `    ``}` `    ``return` `max_len;` `}`   `// Driver code` `int` `main()` `{` `    ``int` `arr[] = { 1, 2, 3, 4, 5 };` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(``int``);` `    ``int` `k = 10;`   `    ``cout << solve(arr, n, k);`   `    ``return` `0;` `}`

## Java

 `// Java implementation of the approach ` `class` `GFG ` `{` `    `  `    ``// Function to return the maximum sum ` `    ``// in a subarray of size k ` `    ``static` `int` `maxSum(``int` `arr[], ``int` `n, ``int` `k) ` `    ``{ ` `        ``// k must be greater ` `        ``if` `(n < k) ` `        ``{ ` `            ``return` `-``1``; ` `        ``} ` `    `  `        ``// Compute sum of first window of size k ` `        ``int` `res = ``0``; ` `        ``for` `(``int` `i = ``0``; i < k; i++) ` `            ``res += arr[i]; ` `    `  `        ``// Compute sums of remaining windows by ` `        ``// removing first element of previous ` `        ``// window and adding last element of ` `        ``// current window. ` `        ``int` `curr_sum = res; ` `        ``for` `(``int` `i = k; i < n; i++) ` `        ``{ ` `            ``curr_sum += arr[i] - arr[i - k]; ` `            ``res = Math.max(res, curr_sum); ` `        ``} ` `    `  `        ``return` `res; ` `    ``} ` `    `  `    ``// Function to return the length of subarray ` `    ``// Sum of all the subarray of this ` `    ``// length is less than or equal to K ` `    ``static` `int` `solve(``int` `arr[], ``int` `n, ``int` `k) ` `    ``{ ` `        ``int` `max_len = ``0``, l = ``0``, r = n, m; ` `    `  `        ``// Binary search from l to r as all the ` `        ``// array elements are positive so that ` `        ``// the maximum subarray sum is monotonically ` `        ``// increasing ` `        ``while` `(l <= r)` `        ``{ ` `            ``m = (l + r) / ``2``; ` `    `  `            ``// Check if the subarray sum is ` `            ``// greater than K or not ` `            ``if` `(maxSum(arr, n, m) > k) ` `                ``r = m - ``1``; ` `            ``else` `            ``{ ` `                ``l = m + ``1``; ` `    `  `                ``// Update the maximum length ` `                ``max_len = m; ` `            ``} ` `        ``} ` `        ``return` `max_len; ` `    ``} ` `    `  `    ``// Driver code ` `    ``public` `static` `void` `main (String[] args) ` `    ``{ ` `        ``int` `arr[] = { ``1``, ``2``, ``3``, ``4``, ``5` `}; ` `        ``int` `n = arr.length; ` `        `  `        ``int` `k = ``10``; ` `    `  `        ``System.out.println(solve(arr, n, k)); ` `    ``} ` `}`   `// This code is contributed by AnkitRai01`

## Python3

 `# Python3 implementation of the approach `   `# Function to return the maximum sum ` `# in a subarray of size k ` `def` `maxSum(arr, n, k) :`   `    ``# k must be greater ` `    ``if` `(n < k) :` `        ``return` `-``1``; `   `    ``# Compute sum of first window of size k ` `    ``res ``=` `0``; ` `    `  `    ``for` `i ``in` `range``(k) :` `        ``res ``+``=` `arr[i]; `   `    ``# Compute sums of remaining windows by ` `    ``# removing first element of previous ` `    ``# window and adding last element of ` `    ``# current window. ` `    ``curr_sum ``=` `res; ` `    `  `    ``for` `i ``in` `range``(k, n) :` `        ``curr_sum ``+``=` `arr[i] ``-` `arr[i ``-` `k]; ` `        ``res ``=` `max``(res, curr_sum); `   `    ``return` `res; `   `# Function to return the length of subarray ` `# Sum of all the subarray of this ` `# length is less than or equal to K ` `def` `solve(arr, n, k) :`   `    ``max_len ``=` `0``; l ``=` `0``; r ``=` `n;`   `    ``# Binary search from l to r as all the ` `    ``# array elements are positive so that ` `    ``# the maximum subarray sum is monotonically ` `    ``# increasing ` `    ``while` `(l <``=` `r) :` `        ``m ``=` `(l ``+` `r) ``/``/` `2``; `   `        ``# Check if the subarray sum is ` `        ``# greater than K or not ` `        ``if` `(maxSum(arr, n, m) > k) :` `            ``r ``=` `m ``-` `1``; ` `        ``else` `:` `            ``l ``=` `m ``+` `1``; `   `            ``# Update the maximum length ` `            ``max_len ``=` `m; ` `            `  `    ``return` `max_len; `   `# Driver code ` `if` `__name__ ``=``=` `"__main__"` `: `   `    ``arr ``=` `[ ``1``, ``2``, ``3``, ``4``, ``5` `]; ` `    ``n ``=` `len``(arr); ` `    ``k ``=` `10``; `   `    ``print``(solve(arr, n, k)); `   `# This code is contributed by AnkitRai01`

## C#

 `// C# implementation of the approach ` `using` `System;`   `class` `GFG ` `{` `    `  `    ``// Function to return the maximum sum ` `    ``// in a subarray of size k ` `    ``static` `int` `maxSum(``int` `[]arr, ``int` `n, ``int` `k) ` `    ``{ ` `        ``// k must be greater ` `        ``if` `(n < k) ` `        ``{ ` `            ``return` `-1; ` `        ``} ` `    `  `        ``// Compute sum of first window of size k ` `        ``int` `res = 0; ` `        ``for` `(``int` `i = 0; i < k; i++) ` `            ``res += arr[i]; ` `    `  `        ``// Compute sums of remaining windows by ` `        ``// removing first element of previous ` `        ``// window and adding last element of ` `        ``// current window. ` `        ``int` `curr_sum = res; ` `        ``for` `(``int` `i = k; i < n; i++) ` `        ``{ ` `            ``curr_sum += arr[i] - arr[i - k]; ` `            ``res = Math.Max(res, curr_sum); ` `        ``} ` `        ``return` `res; ` `    ``} ` `    `  `    ``// Function to return the length of subarray ` `    ``// Sum of all the subarray of this ` `    ``// length is less than or equal to K ` `    ``static` `int` `solve(``int` `[]arr, ``int` `n, ``int` `k) ` `    ``{ ` `        ``int` `max_len = 0, l = 0, r = n, m; ` `    `  `        ``// Binary search from l to r as all the ` `        ``// array elements are positive so that ` `        ``// the maximum subarray sum is monotonically ` `        ``// increasing ` `        ``while` `(l <= r)` `        ``{ ` `            ``m = (l + r) / 2; ` `    `  `            ``// Check if the subarray sum is ` `            ``// greater than K or not ` `            ``if` `(maxSum(arr, n, m) > k) ` `                ``r = m - 1; ` `            ``else` `            ``{ ` `                ``l = m + 1; ` `    `  `                ``// Update the maximum length ` `                ``max_len = m; ` `            ``} ` `        ``} ` `        ``return` `max_len; ` `    ``} ` `    `  `    ``// Driver code ` `    ``public` `static` `void` `Main () ` `    ``{ ` `        ``int` `[]arr = { 1, 2, 3, 4, 5 }; ` `        ``int` `n = arr.Length; ` `        `  `        ``int` `k = 10; ` `    `  `        ``Console.WriteLine(solve(arr, n, k)); ` `    ``} ` `}`   `// This code is contributed by AnkitRai01`

## Javascript

 ``

Output

`2`

Time Complexity: O(N*logN), as we are using binary search which will cost logN and in each traversal, we are calling the function maxSum which will cost O(N) time. Where N is the number of elements in the array.
Auxiliary Space: O(1), as we are not using any extra space.

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