DATA STRUCTURES • ALGORITHMS

Fixed Window Sum

The Sliding Window technique is used to find the maximum sum of any contiguous subarray of size K.

Time

O(N)

Space

O(1)

Key Principle 1

Initial window of size K

Key Principle 2

Slide window by adding one and removing one

Key Principle 3

Constant time updates (O(1) per slide)

Key Principle 4

Optimal for contiguous subproblems

WINDOW_SUM_LAB
Current Step
Goal: Find max sum of subarray of size K=3. Starting with first window.
Playback
Window Monitor ⠿
Current Sum0
Max Sum0
K = 3 | Range: [0 to 2]
Sliding Logic ⠿
1int maxSum = 0, currentSum = 0;
2for (int i = 0; i < k; i++) currentSum += nums[i];
3maxSum = currentSum;
4for (int i = k; i < n; i++) {
5    currentSum += nums[i] - nums[i - k];
6    maxSum = Math.max(maxSum, currentSum);
7}
8return maxSum;
2
[0]
1
[1]
5
[2]
1
[3]
3
[4]
2
[5]
Current Window Sum
0

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