The DSA Toolkit: #1 Sliding Window Format

Manav Verma — Mon, 03 Nov 2025 23:10:05 +0000

How to identify a Problem is a Sliding window problem?

It is an Array or a String question.
Subarray or Substring is asked in the question.
Either windowSize or windowCondition is given (and the other one is asked).
Identify the format of the problem: fixed-size Sliding Window or variable-sized window.
Also, the window size is calculated windowSize = (j-i+1) for any interval.

So, we have two types of sliding window questions: first, a fixed-sized window whose size is explicitly stated in the question; and second, a variable-sized window whose size is not specified in the question and depends on a condition given in the question.

1. Fixed-Size Sliding Window Format

In these types of questions, the window size will be given in the question, and we will be asked to either minimize or maximize a stated condition.

For example: “Find the maximum sum of a subarray of size k.” Here, the window size will be “k”, and we have to “maximize the sum” of the subarrays.

windowSize → GIVEN
condition → Maximize or Minimize

int i=0, j=0;
while (j < A.size()) {
    // Do Calculations

    if(windowSize < k) {
        // Increase Window by adding more elements
    } else if (windowSize == k){
        // Get answer from the calculations

        // Remove the calculations for element `i` (Window start element)
        // Slide Window from i gradually
    }
}
windowSize -> GIVEN
Condition -> MAXIMIZE

Problems:

2. Variable-size Sliding Window Format

In these types of questions, the window size is not specified. Instead, a condition is stated, and we have to either maximize or minimize the window based on that..

For example: “Find the Longest subarray with sum K.” Here, the condition is explicitly stated in the question that the sum should be equal to “k” (sum == k), and we have to “maximize” the window, i.e., find the longest subarray.

condition → GIVEN
windowSize → Maximize or Minimize

int i=0, j=0;
while (j < A.size()) {
    // Do Calculations

    if(condition < k) {
        // Increase Window if condition not met

    } else if (condition == k){
        // Get answer from calculations
        j++;
    } else { // condition >k
            while(condition >k){
                // Remove the calculations for element `i` (Window Start)
                // Slide Window from i
            }

            // Check answer at this point as well
            j++;
    }
}

DEV Community: Manav Verma

The DSA Toolkit: #1 Sliding Window Format

1. Fixed-Size Sliding Window Format

Problems:

2. Variable-size Sliding Window Format

Problems: