Suppose we have a 2D board containing X and O. Capture all regions surrounded by X. A region is captured by changing all Os into Xs in that surrounded region.
X | X | X | X |
X | O | O | X |
X | X | O | X |
X | O | X | X |
After running the output will be
X | X | X | X |
X | X | X | X |
X | X | X | X |
X | O | X | X |
To solve this, we will follow these steps −
- If board is not present, then return blank board
- for i in range 0 to number of rows – 1 −
- if board[i, 0] = ‘O’, then make_one(board, i, 0)
- if board[i, length of row - 1] = ‘O’, then make_one(board, i, length of row – 1)
- for i in range 0 to number of cols – 1 −
- if board[0, i] = ‘O’, then make_one(board, 0, i)
- if board[count of row – 1, i] = ‘O’, then make_one(board, count of row – 1, i)
- for i in range 0 to number of rows
- for j in range 0 to number of cols
- if board[i, j] = ‘O’, then board[i, j] = ‘X’, otherwise for 1, board[i, j] = ‘O’
- for j in range 0 to number of cols
- The make_one will be like −
- if i < 0 or j < 0 or i >= row count or j >= col count or board[i, j] = ‘X’ or board[i, j] = ‘1’, then return
- board[i, j] := 1
- call make_one(voard, i + 1, j), make_one(voard, i - 1, j), make_one(voard, i, j + 1), make_one(voard, i, j - 1)
Let us see the following implementation to get better understanding −
Example
class Solution(object): def solve(self, board): if not board: return board for i in range(len(board)): if board[i][0]=='O': self.make_one(board,i,0) if board[i][len(board[0])-1] == 'O': self.make_one(board,i,len(board[0])-1) for i in range(len(board[0])): if board[0][i]=='O': self.make_one(board,0,i) if board[len(board)-1][i] == 'O': self.make_one(board,len(board)-1,i) for i in range(len(board)): for j in range(len(board[i])): if board[i][j]=='O': board[i][j]='X' elif board[i][j]=='1': board[i][j]='O' return board def make_one(self, board,i,j): if i<0 or j<0 or i>=len(board) or j>=len(board[0]) or board[i][j]=='X' or board[i] [j]=='1': return board[i][j]='1' self.make_one(board,i+1,j) self.make_one(board,i-1,j) self.make_one(board,i,j+1) self.make_one(board,i,j-1) ob1 = Solution() print(ob1.solve([["X","X","X","X"],["X","O","O","X"],["X","X","O","X"],["X","O","X","X"]]))
Input
[["X","X","X","X"],["X","O","O","X"],["X","X","O","X"],["X","O","X","X"]]
Output
[['X', 'X', 'X', 'X'], ['X', 'X', 'X', 'X'], ['X', 'X', 'X', 'X'], ['X', 'O', 'X', 'X']]