Create SurroundedRegions.cpp

SurroundedRegions.cpp

@@ -0,0 +1,58 @@
+/*
+Given a 2D board containing 'X' and 'O' (the letter O), capture all regions surrounded by 'X'.
+
+A region is captured by flipping all 'O's into 'X's in that surrounded region.
+
+Example:
+
+X X X X
+X O O X
+X X O X
+X O X X
+After running your function, the board should be:
+
+X X X X
+X X X X
+X X X X
+X O X X
+*/
+class Solution {
+public:
+    void check(vector<vector<char>>& board,int i,int j){
+      int m=board.size();
+      int n=board[0].size();
+      if(i<0 || j<0 || i>=m || j>=n) return;
+      if(board[i][j]=='O')
+        board[i][j]='*';
+      else return;        
+      check(board,i+1,j);
+      check(board,i-1,j);
+      check(board,i,j+1);
+      check(board,i,j-1);
+    }
+    void solve(vector<vector<char>>& board) {
+      int m=board.size();
+      if(m==0) return;
+      int n=board[0].size();
+      for(int i=0;i<m;i++){
+        if(board[i][0]=='O')
+          check(board,i,0);
+        if(board[i][n-1]=='O')
+          check(board,i,n-1);
+      }
+      for(int i=0;i<n;i++){
+        if(board[0][i]=='O')
+          check(board,0,i);
+        if(board[m-1][i]=='O')
+          check(board,m-1,i);
+      }
+      for(int i=0;i<m;i++){
+        for(int j=0;j<n;j++){
+          if(board[i][j]=='O')
+            board[i][j]='X';
+          else if(board[i][j]=='*')
+            board[i][j]='O';
+      }  
+    }
+  }
+};