130. Surrounded Regions

Author: amitbansal7

surrounded-regions.cpp

@@ -0,0 +1,40 @@
+//Runtime: 19 ms
+class Solution {
+public:
+
+    void DFS(vector<vector<char>>&B, int i, int j)
+    {
+        if (i < 0 || j < 0 || i >= B.size() || j >= B[0].size() || B[i][j] != 'O')
+            return;
+
+        B[i][j] = '#';
+        DFS(B, i + 1, j);
+        DFS(B, i - 1, j);
+        DFS(B, i, j + 1);
+        DFS(B, i, j - 1);
+    }
+
+    void solve(vector<vector<char>>& board) {
+        int m = board.size();
+        if (m <= 0)    return;
+        int n = board[0].size();
+        if (n <= 0)    return;
+
+        for (int i = 0; i < m; i++)
+            for (int j = 0; j < n; j++)
+                if ((i == 0 || i == m - 1 || j == 0 || j == n - 1) && (board[i][j] == 'O'))
+                    DFS(board, i, j);
+
+
+        for (int i = 0; i < m; i++)
+            for (int j = 0; j < n; j++)
+                if (board[i][j] == 'O')
+                    board[i][j] = 'X';
+
+        for (int i = 0; i < m; i++)
+            for (int j = 0; j < n; j++)
+                if (board[i][j] == '#')
+                    board[i][j] = 'O';
+
+    }
+};