Sliding window technique is useful for solving problems involving subarray or substring.

These problems might involve finding the maximum/minimum sum, count of elements satisfying certain conditions, or finding subarrays with specific properties.

Genrally enumerating all substrings/subarrays take O(n^2) time ,But with sliding window algorithm we can reduce that to O(n) time.

Two types Sliding Window :

1. Fixed size
2. Variable size

1.🔥Fixed Size Window

////credits fot template @imanishkumar7545 
fixed_Size_window()
{
    int low = 0, high = 0, windowsize = k;
    while (i < sizeofarray)
    {
        // Step 1: Create a window that is one element smaller than the desired window size
        if (high - low + 1 < windowsize)
        {
            // Generate the window by increasing the high index
            high++;
        }
        // Step 2: Process the window
        else
        {
            // Window size is now equal to the desired window size
            // Step 2a: Calculate the answer based on the elements in the window
            // Step 2b: Remove the oldest element (at low index) from the window for the next window

            // Proceed to the next window by incrementing the low and high indices
        }
    }
}

Basic Slding Window Fixed Size

https://leetcode.com/problems/contains-duplicate-ii (E) Adjacent k Neighbours process
https://leetcode.com/problems/maximum-average-subarray-i/
https://leetcode.com/problems/substrings-of-size-three-with-distinct-characters/
https://leetcode.com/problems/maximum-number-of-vowels-in-a-substring-of-given-length/
https://leetcode.com/problems/maximum-points-you-can-obtain-from-cards/ (M) Convert to sliding window
https://leetcode.com/problems/defuse-the-bomb/ E
https://leetcode.com/problems/substring-with-concatenation-of-all-words H
https://leetcode.com/problems/repeated-dna-sequences/ Map of strings fixed window [Best approach Bit manipulation] ✏️

Deque

https://leetcode.com/problems/sliding-window-maximum ✏️
First negative integer in every window of size k [G]

2.🔥Variable size

2a. Standard Sliding Window

• Standard SW uses a variable INTEGER that represents the window

209. Minimum Size Subarray Sum
713. Subarray Product Less Than K
930. Binary Subarrays With Sum Standard SW with atmost concept | One pass SW | Prefix sum approach
1248. Count Number of Nice Subarrays ✏️
1658. Minimum Operations to Reduce X to Zero Reducible to standard SW
1004. Max Consecutive Ones III ✏️
2024. Maximize the Confusion of an Exam ✏️ Two Pass SW | One Pass SW
2962. Count Subarrays Where Max Element Appears at Least K Times | 1. Atleast k = Total subArray - Atmost k-1 |
1208. Get Equal Substrings Within Budget

2b. Hashmap+Sliding Window
This type of problems require a hashmap or a frequency array to represent a Window

3. Longest Substring Without Repeating Characters
159.Longest Substring with At Most Two Distinct Characters [Premium/CN]
340.Longest Substring with At Most K Distinct Characters[Premium/CN]
3090. Maximum Length Substring With Two Occurrences
76. Minimum Window Substring (HARD)
424. Longest Repeating Character Replacement Similar concept as LC 1004
438. Find All Anagrams in a String
567. Permutation in String
904. Fruit Into Baskets
1695. Maximum Erasure Value 🔁
2958. Length of Longest Subarray With at Most K Frequency
992. Subarrays with K Different Integers Atmost concept
395. Longest Substring with At Least K Repeating Characters ⚠️☠️🚨

2c. PrefixSum+HashMap+Sliding Window

https://leetcode.com/problems/maximum-erasure-value/ 🔁

2d. Bit Manipulation

2401. Longest Nice Subarray BITMASKING + SW ✏️

2e. Greedy

1838. Frequency of the Most Frequent Element SW+Greedy|Can also be solved using Bin Search + Preffix sum