Day 49 | Surrounded Regions | LeetCode 130 | JavaScript | DFS from Border O's скачать в хорошем качестве

Day 49 | Surrounded Regions | LeetCode 130 | JavaScript | DFS from Border O's

🔥 Day 49 of my LeetCode Daily Challenge! Today we solve LeetCode #130 — Surrounded Regions, a clever Reverse DFS problem where we start DFS from border 'O' cells and work inward using JavaScript! ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 📌 PROBLEM: Surrounded Regions 🔗 https://leetcode.com/problems/surroun... 📊 Difficulty: Medium 🗂️ Topics: Array, DFS, Matrix ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 💡 WHAT YOU'LL LEARN: ✅ The "Border DFS" trick — start DFS from boundary 'O's, not every cell ✅ How to safely identify which 'O's CANNOT be flipped to 'X' ✅ 3-step in-place board modification strategy ✅ Time & Space Complexity Analysis ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 🧠 APPROACH (3-Step Strategy): → Step 1: Scan all BORDER cells — for every 'O' on the border, run DFS to mark all connected 'O's as safe (temp mark 'A') → Step 2: Traverse the entire board: • Any remaining 'O' (not safe) → flip to 'X' (it's surrounded!) • Any 'A' (safe) → restore back to 'O' → Step 3: Done! ✅ 🔑 KEY RULE: An 'O' is SAFE only if it's connected to a border 'O' Any 'O' NOT connected to the border is surrounded → flip to 'X' → Time Complexity: O(M × N) | Space Complexity: O(M × N) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 🔑 KEY INSIGHT: 💡 Don't try to find surrounded regions directly — that's hard! Instead, find what's NOT surrounded (border-connected O's) and protect them. Then flip everything else. This "reverse thinking" is the interview trick! 🚀 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 📚 MY LEETCODE JOURNEY PLAYLIST:    • Leetcode   🤝 CONNECT WITH ME: • GitHub: https://github.com/ashwinikemshetty • LinkedIn:   / ashwinikemshetty   📅 #100DaysOfCode #LeetCodeChallenge 🌟 If this helped you, LIKE 👍, COMMENT 💬 & SUBSCRIBE 🔔! ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ #LeetCode #JavaScript #DSA #Day49 #SurroundedRegions #LeetCode130 #CodingChallenge #ProblemSolving #DFS #BorderDFS #GridTraversal #100DaysOfCode #JavaScriptDeveloper #DataStructures #Algorithms #TechInterview #CodingInterview #MatrixDFS #GraphProblems #CaptureRegions