Maximum sum of k elements

It usessliding_window It must be having [difficulty:: medium], it takes [time complexity:: O(n)].

• Below is the code I was able to write and [time taken:: 20mins]

Break it down

• Lets say we have to find maximum sum of 3 consecutive elements

Code

function maxSum(arr, arrLen, windowSize) {
    let max = 0;
    let sum = 0;
    for (let i = 0; i < windowSize; i++) {
        sum += arr[i];
    }
    max = sum;
    for (let j = windowSize; j < arrLen; j++) {
        // move window, first element reduce from sum, last element of window add to sum, if sum greater assign to max
        let winFirstEl = arr[j-windowSize];
        const winLastEl = arr[j];
        sum += winLastEl - winFirstEl;
        if (sum > max) {
            max = sum;
        }
        
    }
    return max;
}
 
// Driver code
let arr = [1, 4, 2, 10, 2, 3, 1, 0, 20];
let k = 4;
let n = arr.length;
console.log(maxSum(arr, n, k));