using flood fill algorithm

Author: gs146

Sorrounded regions

@@ -0,0 +1,60 @@
+class Solution {
+public:
+    
+    void flood_fill(vector<vector<char>>& board, int x, int y, char prev1,char new1, int m, int n)
+    {
+        if(x<0 || x>=m || y<0 ||y>=n)
+            return;
+        if(board[x][y]!=prev1)
+            return;
+        
+        board[x][y] = new1;
+        
+        //all four directions
+        flood_fill(board,x+1, y, prev1, new1,m,n);
+        flood_fill(board,x-1, y, prev1, new1,m,n);
+        flood_fill(board,x, y+1, prev1, new1,m,n);
+        flood_fill(board,x, y-1, prev1, new1,m,n);
+        
+    }
+    void replace_edges(vector<vector<char>>& board)
+    {
+        
+        int m = board.size();
+        int n = board[0].size();
+        
+        for(int i=0;i<m;i++)
+            for(int j=0;j<n;j++)
+                if(board[i][j]=='O')
+                    board[i][j]='-';
+            
+            for(int i=0;i<m;i++)
+                if(board[i][0]=='-')
+                    flood_fill(board, i, 0, '-', 'O',m,n);
+            
+            for(int i=0;i<n;i++)
+                if(board[0][i]=='-')
+                    flood_fill(board, 0, i, '-', 'O',m,n);
+            
+            for(int i=0;i<m;i++)
+                if(board[i][n-1]=='-')
+                    flood_fill(board, i, n-1, '-', 'O',m,n);
+            
+            for(int i=0;i<n;i++)
+                if(board[m-1][i]=='-')
+                    flood_fill(board, m-1, i, '-', 'O',m,n);
+            
+            for(int i=0;i<m;i++)
+                for(int j=0;j<n;j++)
+                    if(board[i][j]=='-')
+                        board[i][j] = 'X';
+        
+    }
+    void solve(vector<vector<char>>& board) 
+    {
+        if(board.size()==0)
+            return;
+        replace_edges(board);
+        
+    }
+};