Gamify your prep <and>
Ace your
placement

function findMaxSubarraySum(arr, k) { 
  if (arr.length < k) { 
    return null; 
  } 

  let maxSum = 0; 
  let windowSum = 0; 

  // Calculate sum of first k elements 
  for (let i = 0; i < k; i++) { 
    windowSum += arr[i]; 
  } 

  maxSum = windowSum; 

  // Slide window and track maximum 
  for (let i = k; i < arr.length; i++) { 
    windowSum = windowSum - arr[i - k] + arr[i]; 
    maxSum = Math.max(maxSum, windowSum); 
  } 

  return maxSum; 
}