Maximum Sum Subarray Of Length K in JavaScript

Given an input array of integers and a positive integer k, find out the maximum sum of a contiguous subarray of length exactly k

Example

Input: nums = [5, 6, 1, 2, 6, 6, 4, 3], k = 3
Output: 4 6
Explanation: The subarray nums[4...6] has the maximum sum of 16

Understanding the Problem

The core challenge of this problem is to find the maximum sum of any contiguous subarray of length k within the given array. This problem is significant in various applications such as financial analysis, where one might want to find the period with the highest profit.

Potential pitfalls include misunderstanding the requirement for the subarray to be contiguous and not considering edge cases where the array length is less than k.

Approach

To solve this problem, we can use a sliding window approach, which is more efficient than a naive solution.

Naive Solution

The naive solution involves iterating through all possible subarrays of length k and calculating their sums. This approach has a time complexity of O(n*k), which is not optimal for large arrays.

Optimized Solution: Sliding Window

The sliding window technique allows us to calculate the sum of the subarray in O(1) time after the initial sum calculation. This reduces the overall time complexity to O(n).

Here's how it works:

Calculate the sum of the first k elements.
Slide the window one element at a time, adding the next element and subtracting the first element of the previous window.
Keep track of the maximum sum encountered.

Algorithm

Let's break down the sliding window algorithm step-by-step:

Initialize the sum of the first k elements.
Initialize the maximum sum as the sum of the first k elements.
Iterate through the array from the k-th element to the end.
For each element, update the current sum by adding the current element and subtracting the element that is k positions behind.
Update the maximum sum if the current sum is greater.

Code Implementation

// Function to find the maximum sum subarray of length k
function maxSumSubarray(nums, k) {
    // Initialize the sum of the first k elements
    let maxSum = 0;
    for (let i = 0; i < k; i++) {
        maxSum += nums[i];
    }

    // Initialize the current sum to the maxSum
    let currentSum = maxSum;

    // Slide the window from k to the end of the array
    for (let i = k; i < nums.length; i++) {
        // Update the current sum by adding the current element and subtracting the element k positions behind
        currentSum += nums[i] - nums[i - k];
        // Update the maxSum if the current sum is greater
        maxSum = Math.max(maxSum, currentSum);
    }

    return maxSum;
}

// Example usage
const nums = [5, 6, 1, 2, 6, 6, 4, 3];
const k = 3;
console.log(maxSumSubarray(nums, k)); // Output: 16

Complexity Analysis

The time complexity of the sliding window approach is O(n) because we only pass through the array once. The space complexity is O(1) as we are using a constant amount of extra space.

Edge Cases

Consider the following edge cases:

Array length less than k: The function should handle this gracefully, possibly by returning 0 or an error message.
All elements are negative: The function should still return the maximum sum, which might be a negative number.

Testing

To test the solution comprehensively, consider the following test cases:

Simple cases with small arrays.
Arrays with all positive or all negative numbers.
Arrays with mixed positive and negative numbers.
Edge cases where the array length is less than k.

Thinking and Problem-Solving Tips

When approaching such problems, it's essential to:

Understand the problem requirements and constraints thoroughly.
Consider both naive and optimized solutions.
Think about edge cases and how to handle them.
Practice similar problems to improve problem-solving skills.

Conclusion

In this blog post, we discussed how to find the maximum sum subarray of length k using a sliding window approach. This method is efficient and easy to implement, making it a valuable tool for solving similar problems.

Understanding and practicing such problems can significantly enhance your problem-solving skills and prepare you for coding interviews and real-world applications.

Additional Resources

For further reading and practice, consider the following resources:

Maximum Sum Subarray of length K in JavaScript (Time Complexity: O(n))