[leetcode刷题系列]Surrounded Regions

囧， 这题用dfs我re了，应该是爆栈了。 于是改成了bfs就过了

const int MAXN = 1000 + 10;

const int dx[] = {-1, 0, 0, 1};
const int dy[] = {0, -1, 1, 0};

int n, m;
bool vis[MAXN][MAXN];

void bfs(int r, int c, vector<vector<char> > & board){
    queue<pair<int, int> > q;
    q.push(make_pair(r, c));
    vis[r][c] = 1;
    while(!q.empty()){
        r = q.front().first;
        c = q.front().second;
        q.pop();
        for(int p = 0; p < 4; ++ p){
            int nr = r + dx[p];
            int nc = c + dy[p];
            if(nr >= 0 && nr < n)
                if(nc >= 0 && nc < m)
                    if(!vis[nr][nc])
                        if(board[nr][nc] == 'O'){
                            vis[nr][nc] = 1;
                            q.push(make_pair(nr, nc));
                        }
        }
    }
}
class Solution {
public:
    void solve(vector<vector<char>> &board) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(board.size() <= 0 || board[0].size() <= 0)
            return;
        memset(vis, 0x00, sizeof(vis));
        n = board.size();
        m = board[0].size();
        for(int i = 0; i < m; ++ i)
            if(board[0][i] == 'O')
                if(!vis[0][i])
                    bfs(0, i, board);
        for(int i = 0; i< m; ++ i)
            if(board[n - 1][i] == 'O')
                if(!vis[n - 1][i])
                    bfs(n - 1, i, board);
        for(int i = 0; i < n; ++ i)
            if(board[i][0] == 'O')
                if(!vis[i][0])
                    bfs(i, 0, board);
        for(int i = 0; i < n; ++ i)
            if(board[i][m - 1] == 'O')
                if(!vis[i][m - 1])
                    bfs(i, m - 1, board);
        for(int i = 0; i < n; ++ i)
            for(int j = 0; j < m; ++ j)
                if(board[i][j] == 'O')
                    if(!vis[i][j])
                        board[i][j] = 'X';
    }
};