LeetCode 999. Available Captures for Rook

Description

https://leetcode.com/problems/available-captures-for-rook/

On an 8 x 8 chessboard, there is exactly one white rook 'R' and some number of white bishops 'B', black pawns 'p', and empty squares '.'.

When the rook moves, it chooses one of four cardinal directions (north, east, south, or west), then moves in that direction until it chooses to stop, reaches the edge of the board, captures a black pawn, or is blocked by a white bishop. A rook is considered attacking a pawn if the rook can capture the pawn on the rook’s turn. The number of available captures for the white rook is the number of pawns that the rook is attacking.

Return the number of available captures for the white rook.

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'

Explanation

Find rook position, and then start from rook position to find captures.

Python Solution

class Solution:
    def numRookCaptures(self, board: List[List[str]]) -> int:
        rook_position = [-1, -1]
        
        for i in range(len(board)):
            for j in range(len(board[0])):
                if board[i][j] == 'R':
                    rook_position[0] = i
                    rook_position[1] = j
                    

        count = 0
        for i in range(rook_position[0] - 1, -1, -1):     
            if board[i][rook_position[1]] != '.' and board[i][rook_position[1]] != 'p':
                break
            if board[i][rook_position[1]] == 'p':
                count += 1
                break

        for i in range(rook_position[0] + 1, len(board)):                
            if board[i][rook_position[1]] != '.' and board[i][rook_position[1]] != 'p':
                break
            if board[i][rook_position[1]] == 'p':
                count += 1
                break
                
        
        for j in range(rook_position[1] - 1, -1, -1):                
            if board[rook_position[0]][j] != '.' and board[rook_position[0]][j] != 'p':
                break
            if board[rook_position[0]][j] == 'p':
                count += 1
                break

        for j in range(rook_position[1] + 1, len(board[0])):                
            if board[rook_position[0]][j] != '.' and board[rook_position[0]][j] != 'p':
                break
            if board[rook_position[0]][j] == 'p':
                count += 1
                break
            
            
        return count
  • Time Complexity: O(N^2)
  • Space Complexity: O(1)

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