Q:

Given a 2D board containing 'X' and 'O', capture all regions surrounded by 'X'.

A region is captured by flipping all 'O's into 'X's in that surrounded region .

For example,

X X X XX O O XX X O XX O X X

 

After running your function, the board should be:

X X X XX X X XX X X XX O X X A: 此题用bfs/dfs都可以解。 首先，从board的四周出发，dfs/bfs遍历，遇到O，作标记，例如'+'---这些O是没有被X包围的O 接着，遍历整个board，遇到O的，这些O是被X包围的O，改成X，遇到特殊标记的，改回O

int m,n;   void solve(vector
     
      
       > &board) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(board.empty()||board[0].empty())            return;        m = board.size();        n = board[0].size();        for(int j=0;j
       
        >& board)    {        if(nrow>=m||nrow<0||ncol<0||ncol>=n||board[nrow][ncol]!='O')            return;        board[nrow][ncol] = '+';        dfs(nrow+1,ncol,board);        dfs(nrow-1,ncol,board);        dfs(nrow,ncol-1,board);        dfs(nrow,ncol+1,board);    }