📌 FAANG Coding Patterns Series – Day 1

Sliding Window Mastery (Fixed + Variable)

🔹 Why Sliding Window?

Sliding window is one of the most universal FAANG patterns.

Google: loves optimizing substrings & arrays with O(n).
Amazon: standard repetition of substring/array window.
Meta (Facebook): focuses on variable windows with conditions.
Apple: adds edge constraints (like k-size + max/min).
Netflix: applies it in streaming/log analysis contexts.

🔹 Two Core Templates

1. Fixed-Size Sliding Window

Used when window length is known (like k).

int slidingWindowFixed(int[] arr, int k) {
    int left = 0, sum = 0, maxSum = 0;
    for (int right = 0; right < arr.length; right++) {
        sum += arr[right];

        if (right - left + 1 > k) {
            sum -= arr[left];
            left++;
        }
        maxSum = Math.max(maxSum, sum);
    }
    return maxSum;
}

2. Variable-Size Sliding Window

Used when window grows/shrinks based on condition.

int slidingWindowVariable(String s) {
    int left = 0, maxLen = 0;
    Map<Character, Integer> map = new HashMap<>();

    for (int right = 0; right < s.length(); right++) {
        char c = s.charAt(right);
        map.put(c, map.getOrDefault(c, 0) + 1);

        while (map.get(c) > 1) {  // shrink if invalid
            char leftChar = s.charAt(left);
            map.put(leftChar, map.get(leftChar) - 1);
            left++;
        }

        maxLen = Math.max(maxLen, right - left + 1);
    }
    return maxLen;
}

🔹 Flagship Problems

✅ Google / Amazon – Longest Substring Without Repeating Characters

Input: "abcabcbb" → Output: 3 ("abc")
Uses variable window + hash map.

✅ Meta (Facebook) / Google – Minimum Window Substring

Input: S = "ADOBECODEBANC", T = "ABC" → Output: "BANC"
Uses two-pointer shrink + frequency map.

✅ Apple / Netflix – Sliding Window Maximum

Input: [1,3,-1,-3,5,3,6,7], k = 3 → Output: [3,3,5,5,6,7]
Uses Deque (Monotonic Queue).

🔹 Company-Specific Insights

Google: Might push for substring problems with twists (palindrome, k replacements).
Amazon: Loves variations of longest substring with condition.
Meta: Adds constraints like at most k distinct characters.
Apple: Loves max/min inside fixed window → Deque trick.
Netflix: Streaming logs → moving averages, anomaly detection with sliding window.