From 5cef856496227e91157c700becfac4d9c570c5e8 Mon Sep 17 00:00:00 2001
From: Fazeel Usmani <fazeelusmani18@gmail.com>
Date: Mon, 1 Nov 2021 20:58:06 +0530
Subject: [PATCH] Create 01_surroundedRegions.cpp

---
 .../01_surroundedRegions.cpp                  | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 11 November Leetcode Challenge 2021/01_surroundedRegions.cpp

diff --git a/11 November Leetcode Challenge 2021/01_surroundedRegions.cpp b/11 November Leetcode Challenge 2021/01_surroundedRegions.cpp
new file mode 100644
index 0000000..1989e67
--- /dev/null
+++ b/11 November Leetcode Challenge 2021/01_surroundedRegions.cpp	
@@ -0,0 +1,36 @@
+class Solution {
+public:
+    void DFS(vector<vector<char>>& board, int x, int y, char c) {
+        if (x < 0 || x >= board.size() || y < 0 || y >= board[0].size() || board[x][y] != 'O') return;
+            
+        board[x][y] = c;
+        
+        DFS(board, x + 1, y, c);
+        DFS(board, x - 1, y, c);
+        DFS(board, x, y + 1, c);
+        DFS(board, x, y - 1, c);
+    }
+    
+    void solve(vector<vector<char>>& board) {
+        int n = board.size(), m = board[0].size();
+        
+        // Change the 'O's connected to border to '!'
+        for (int i = 0; i < n; i++) {
+            if (board[i][0] == 'O') DFS(board, i, 0, '!');
+            if (board[i][m-1] == 'O') DFS(board, i, m-1, '!');
+        }
+        
+        for (int i = 0; i < m; i++) {
+            if (board[0][i] == 'O') DFS(board, 0, i, '!');
+            if (board[n-1][i] == 'O') DFS(board, n-1, i, '!');
+        }
+        
+        // Change all remaining 'O's to 'x' and '!' back to 'O'
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                if (i && j && i < n - 1 && j < m - 1 && board[i][j] == 'O') board[i][j] = 'X';
+                if (board[i][j] == '!') board[i][j] = 'O';
+            }
+        }
+    }
+};