130. Surrounded Regions

130. Surrounded Regions

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.

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

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思路：如果边缘有'O'，则先把'O'附近的所有关联的'O'记作1，然后剩余的'O'就是被包围的，变化为X，再把1->O。

         X X X X           X X X X             X X X X         X X O X  ->       X X O X    ->       X X X X         X O X X           X 1 X X             X O X X         X O X X           X 1 X X             X O X X

class Solution {    void check(vector<vector<char>> & board, int i,int j, int row, int col)    {        if(board[i][j]=='O'){            board[i][j]='1';            if(i>1)            check(board,i-1,j,row,col);            if(j>1)            check(board,i,j-1,row,col);            if(i+1<row)            check(board,i+1,j,row,col);            if(j+1<col)            check(board,i,j+1,row,col);        }    }public:    void solve(vector<vector<char>>& board) {        int m=board.size();        if(!m) return;        int n=board[0].size();        for(int i=0;i<m;i++)        {            check(board,i,0,m,n);            if(n>1)            check(board,i,n-1,m,n);        }        for(int j=1;j+1<n;j++)        {            check(board,0,j,m,n);            if(m>1)            check(board,m-1,j,m,n);        }        for(int i=0;i<m;i++)        for(int j=0;j<n;j++)        {            //if(board[i][j]=='1') board[i][j]='O';            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]=='1') board[i][j]='O';           // if(board[i][j]=='O') board[i][j]='X';        }        return;    }};