Surrounded Regions

Description：

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 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

Code：

 1 struct vertex

 2 {

 3     int row;

 4     int col;

 5     vertex (int x, int y):row(x),col(y)

 6     {

 7         

 8     }

 9 };

10 

11   void BFSTraverse (vector< vector<char> >& board, int i, int j)

12   {//因为值被修改为'S'就说明该元素已被访问，所以本题中可以不用另外的变量记录访问状态

13             board[i][j] = 'S';

14             deque<vertex>m;

15             m.push_back( vertex(i,j) );

16             while ( !m.empty() )

17             {

18                    vertex v = m.front();

19                    m.pop_front();

20 

21                    int mRow = v.row-1;

22                    if ( mRow >=0 && board[mRow][v.col] == 'O')

23                     {//上面的元素

24                            board[mRow][v.col] = 'S';

25                            m.push_back( vertex(mRow, v.col) );

26                    }

27                    mRow = v.row+1;

28                    if ( mRow < board.size() && board[mRow][v.col] == 'O')

29                    {//下面的元素

30                            board[mRow][v.col] = 'S';

31                            m.push_back( vertex(mRow, v.col) );

32                    }

33                    int mCol = v.col - 1;

34                    if ( mCol >=0 && board[v.row][mCol] == 'O')

35                    {//左面的元素

36                            board[v.row][mCol] = 'S';

37                            m.push_back( vertex(v.row, mCol));

38                    }

39                     mCol = v.col + 1;

40                    if ( mCol < board[0].size()  && board[v.row][mCol] == 'O' )

41                    {//右面的元素

42                            board[v.row][mCol] = 'S';

43                            m.push_back( vertex(v.row, mCol));

44                    }

45            }

46   }

47     

48     void solve(vector< vector<char> >& board)

49     {

50         int row = board.size();

51         if ( row!=0 )

52         {

53             int col = board[0].size();

54             for (int j = 0; j < col; ++j)

55            {

56                 if ( board[0][j] == 'O')

57                     BFSTraverse (board, 0, j);

58                 if ( board[row-1][j] == 'O')

59                     BFSTraverse (board, row-1, j);

60            }

61            for (int i = 1;  i < row-1; ++i)

62            {

63                if ( board[i][0] == 'O')

64                     BFSTraverse (board, i, 0);

65                 if ( board[i][col-1] == 'O' )

66                     BFSTraverse (board, i, col-1);

67            }

68            

69            for (int  i = 0; i < row; ++i )

70            {

71                for ( int j = 0; j < col; ++j )

72                {

73                    if (board[i][j] == 'S')

74                         board[i][j] = 'O';

75                    else if (board[i][j] == 'O')

76                         board[i][j] = 'X';

77                    else

78                    ;

79                }

80            }//for

81         }//if

82     }