999. Available Captures for Rook

Problem Link

Description

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You are given an 8 x 8 matrix representing a chessboard. There is exactly one white rook represented by 'R', some number of white bishops 'B', and some number of black pawns 'p'. Empty squares are represented by '.'.

A rook can move any number of squares horizontally or vertically (up, down, left, right) until it reaches another piece or the edge of the board. A rook is attacking a pawn if it can move to the pawn's square in one move.

Note: A rook cannot move through other pieces, such as bishops or pawns. This means a rook cannot attack a pawn if there is another piece blocking the path.

Return the number of pawns the white rook is attacking.

 

Example 1:

Input: board = [[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".","R",".",".",".","p"],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."]]

Output: 3

Explanation:

In this example, the rook is attacking all the pawns.

Example 2:

Input: board = [[".",".",".",".",".",".","."],[".","p","p","p","p","p",".","."],[".","p","p","B","p","p",".","."],[".","p","B","R","B","p",".","."],[".","p","p","B","p","p",".","."],[".","p","p","p","p","p",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."]]

Output: 0

Explanation:

The bishops are blocking the rook from attacking any of the pawns.

Example 3:

Input: board = [[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".","p",".",".",".","."],["p","p",".","R",".","p","B","."],[".",".",".",".",".",".",".","."],[".",".",".","B",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".",".",".",".",".","."]]

Output: 3

Explanation:

The rook is attacking the pawns at positions b5, d6, and f5.

 

Constraints:

• board.length == 8
• board[i].length == 8
• board[i][j] is either 'R', '.', 'B', or 'p'
• There is exactly one cell with board[i][j] == 'R'

Solution

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Python3

class Solution:
    def numRookCaptures(self, board: List[List[str]]) -> int:
        x = y = 0
        
        for i in range(8):
            for j in range(8):
                if board[i][j] == 'R':
                    x, y = i, j
        
        left, right = y - 1, y + 1
        top, bottom = x - 1, x + 1
        res = 0
        
        while left >= 0:
            if board[x][left] == ".":
                left -= 1
            elif board[x][left] == "B":
                break
            elif board[x][left] == "p":
                res += 1
                break
        
        while right < 8:
            if board[x][right] == ".":
                right += 1
            elif board[x][right] == "B":
                break
            elif board[x][right] == "p":
                res += 1
                break
        
        while top >= 0:
            if board[top][y] == ".":
                top -= 1
            elif board[top][y] == "B":
                break
            elif board[top][y] == "p":
                res += 1
                break
        
        while bottom < 8:
            if board[bottom][y] == ".":
                bottom += 1
            elif board[bottom][y] == "B":
                break
            elif board[bottom][y] == "p":
                res += 1
                break
        
        return res