130. Surrounded Regions

README.md

@@ -341,7 +341,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 743  | [Network Delay Time](https://leetcode.com/problems/network-delay-time/)                                                                                           | [C++](./C++/Network-delay-time.cpp)                                              | _O(V+E))_                 | O(V)              | Medium     | BFS |
 | 111  | [Min Depth of Binary Tree](https://leetcode.com/problems/minimum-depth-of-binary-tree/)                                                                           | [JavaScript](./JavaScript/111-minimum-depth-of-binary-tree.js)                   | O(nlogn)                  | O(nlogn)          | Easy       | BFS |
 | 100  | [Same Tree](https://leetcode.com/problems/same-tree/)                                                                                                             | [C++](https://github.com/codedecks-in/LeetCode-Solutions/blob/master/C%2B%2B/100_Same_Tree.cpp) | O(N)       | O(N)              | Easy       | BFS | 
-
+| 130 | [Surrounded Regions](https://leetcode.com/problems/surrounded-regions/)                                       | [C++](./C++/kth-smallest-element-in-a-bst.cpp)                  | _O(m*n)_ | _O(m*n)_ | Medium     | DFS |      |                                                                                                            
 
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@@ -515,6 +515,7 @@ DISCLAIMER: This above mentioned resources have affiliate links, which means if
 | [Shrimadh V Rao](https://github.com/Shrimadh) <br> <img src="https://avatars.githubusercontent.com/u/64469917?v=4" width="100" height="100">                                                                   | India          | C++                  |  [GitHub](https://github.com/Shrimadh)
 | [Shreyas Shrawage](https://github.com/shreyventure) <br> <img src = "https://avatars.githubusercontent.com/u/55741087?v=4" width="100" height="100"> | India | Python | [CodeChef](https://www.codechef.com/users/shreyventure)<br/>[LeetCode](https://leetcode.com/shreyventure/)<br/>[HackerRank](https://www.hackerrank.com/shreyas_shrawage)
 | [Surbhi Mayank](https://github.com/surbhi2408) <br> <img src="https://avatars.githubusercontent.com/u/58289829?s=400&u=68fd396819b927ec4d8820d87d6d1e311c3abd01&v=4" width="100" height="100">                                                                   | India          | C++                  |  [GitHub](https://github.com/surbhi2408)
+| [Nick H](https://github.com/n1i9c9k9) <br> <img src="https://github.com/n1i9c9k9.png" width="100" height="100">                                                                   | Germany          | C++                  |  [GitHub](https://github.com/n1i9c9k9)
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 </div>

surrounded-regions.cpp

@@ -0,0 +1,64 @@
+#include <vector>
+#include <queue>
+
+class Solution {
+public:
+    void solve(std::vector<std::vector<char>>& board) {
+        if (board.empty() || board[0].empty()) return;
+
+        int m = board.size();
+        int n = board[0].size();
+
+        // Directions for moving up, down, left, right
+        std::vector<std::pair<int, int>> directions = {
+            {1, 0},  // down
+            {0, 1},  // right
+            {0, -1}, // left
+            {-1, 0}  // up
+        };
+
+        // BFS function to mark all connected 'O's
+        auto bfs = [&](int startY, int startX) {
+            std::queue<std::pair<int, int>> q;
+            q.push({startY, startX});
+            board[startY][startX] = 'E'; // Mark as visited with 'E'
+
+            while (!q.empty()) {
+                auto [y, x] = q.front();
+                q.pop();
+
+                for (const auto& dir : directions) {
+                    int newY = y + dir.first;
+                    int newX = x + dir.second;
+
+                    if (newY >= 0 && newY < m && newX >= 0 && newX < n && board[newY][newX] == 'O') {
+                        board[newY][newX] = 'E'; // Mark as visited
+                        q.push({newY, newX});    // Add to queue
+                    }
+                }
+            }
+        };
+
+        // Check all edge 'O's
+        for (int i = 0; i < n; ++i) {
+            if (board[0][i] == 'O') bfs(0, i);        // Top row
+            if (board[m - 1][i] == 'O') bfs(m - 1, i); // Bottom row
+        }
+
+        for (int j = 1; j < m - 1; ++j) {
+            if (board[j][0] == 'O') bfs(j, 0);        // Left column
+            if (board[j][n - 1] == 'O') bfs(j, n - 1); // Right column
+        }
+
+        // Update the board: 'O's not connected to the edges become 'X', and 'E's back to 'O'
+        for (int i = 0; i < m; ++i) {
+            for (int j = 0; j < n; ++j) {
+                if (board[i][j] == 'O') {
+                    board[i][j] = 'X'; // Flip 'O's to 'X's
+                } else if (board[i][j] == 'E') {
+                    board[i][j] = 'O'; // Restore 'E's back to 'O's
+                }
+            }
+        }
+    }
+};