Available Captures for Rook - Array - Easy - LeetCode

On an 8 x 8 chessboard, there is one white rook. There also may be empty squares, white bishops, and black pawns. These are given as characters 'R', '.', 'B', and 'p' respectively. Uppercase characters represent white pieces, and lowercase characters represent black pieces.

The rook moves as in the rules of Chess: it chooses one of four cardinal directions (north, east, west, and south), then moves in that direction until it chooses to stop, reaches the edge of the board, or captures an opposite colored pawn by moving to the same square it occupies. Also, rooks cannot move into the same square as other friendly bishops.

Return the number of pawns the rook can capture in one move.

Example 1:

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

Output: 3

Explanation:

In this example the rook is able to capture all the pawns.

Example 2:

Input: [[".",".",".",".",".",".",".","."],[".","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:

Bishops are blocking the rook to capture any pawn.

Example 3:

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

Output: 3

Explanation:

The rook can capture the pawns at positions b5, d6 and f5.

Note:

board.length == board[i].length == 8

board[i][j] is either 'R', '.', 'B', or 'p'

There is exactly one cell with board[i][j] == 'R'

Solution:

using System;
using System.Collections.Generic;
using System.Text;

namespace LeetCode.AskGif.Easy.Array
{
 public class NumRookCapturesSoln
 {
 public int NumRookCaptures(char[][] board)
 {
 var whiteRook = 'R'; 

 for (int i = 0; i < board.Length; i++)
 {
 for (int j = 0; j < board[i].Length; j++)
 {
 //check for White Rook
 if(board[i][j]== whiteRook)
 {
 return CalculatePawnsCount(board, i, j);
 }
 }
 }

 return 0;
 }

 private int CalculatePawnsCount(char[][] board, int row, int column)
 {
 var whiteBishop = 'B';
 var blackPawn = 'p';
 var empty = '.';

 int count = 0;

 //UP Count
 for (int i = row-1; i >= 0 && row != 0; i--)
 {
 if(board[i][column] != empty)
 {
 if( board[i][column] == blackPawn)
 {
 count += 1; 
 }
 break;
 }
 }

 //Down Count
 for (int i = row + 1; i < board.Length && row != board.Length-1; i++)
 {
 if (board[i][column] != empty)
 {
 if (board[i][column] == blackPawn)
 {
 count += 1;
 }
 break;
 }
 }

 //Left Count
 for (int i = column - 1; i >= 0 && column != 0; i--)
 {
 if (board[row][i] != empty)
 {
 if (board[row][i] == blackPawn)
 {
 count += 1;
 }
 break;
 }
 }

 //Right Count
 for (int i = column + 1; i < board[row].Length && column != board[row].Length-1; i++)
 {
 if (board[row][i] != empty)
 {
 if (board[row][i] == blackPawn)
 {
 count += 1;
 }
 break;
 }
 }

 return count;
 }
 }
}

Time Complexity: O(m*n) Where m and n are rows and columns of the matrix

Space Complexity: O(1)

Unit Tests:

using LeetCode.AskGif.Easy.Array;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodingUnitTest.Easy.Array
{
 [TestClass]
 public class NumRookCapturesSolnTests
 {
 [TestMethod]
 public void NumRookCapturesSoln_First()
 {
 var board = new string[,]{
 {".", ".", ".", ".", ".", ".", ".", "."},
 {".", ".", ".", "p", ".", ".", ".", "."},
 {".", ".", ".", "R", ".", ".", ".", "p"},
 {".", ".", ".", ".", ".", ".", ".", "."},
 {".", ".", ".", ".", ".", ".", ".", "."},
 {".", ".", ".", "p", ".", ".", ".", "."},
 {".", ".", ".", ".", ".", ".", ".", "."},
 { ".", ".", ".", ".", ".", ".", ".", "."}
 };
 var expected = 3;

 var res = new NumRookCapturesSoln().NumRookCaptures(ArrayMapper(board));
 Assert.AreEqual(expected, res);
 }

 [TestMethod]
 public void NumRookCapturesSoln_Second()
 {
 var board = new string[,]{
 {".", ".", ".", ".", ".", ".", ".", "."},
 {".", "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", ".", "."},
 {".", ".", ".", ".", ".", ".", ".", "."},
 { ".", ".", ".", ".", ".", ".", ".", "."}
 };
 var expected = 0;

 var res = new NumRookCapturesSoln().NumRookCaptures(ArrayMapper(board));
 Assert.AreEqual(expected, res);
 }

 [TestMethod]
 public void NumRookCapturesSoln_Third()
 {
 var board = new string[,]{
 {".", ".", ".", ".", ".", ".", ".", "."},
 {".", ".", ".", "p", ".", ".", ".", "."},
 {".", ".", ".", "p", ".", ".", ".", "."},
 {"p", "p", ".", "R", ".", "p", "B", "."},
 {".", ".", ".", ".", ".", ".", ".", "."},
 {".", ".", ".", "B", ".", ".", ".", "."},
 {".", ".", ".", "p", ".", ".", ".", "."},
 { ".", ".", ".", ".", ".", ".", ".", "."}
 };
 var expected = 3;

 var res = new NumRookCapturesSoln().NumRookCaptures(ArrayMapper(board));
 Assert.AreEqual(expected, res);
 }

 private char[][] ArrayMapper(string[,] matrix)
 {
 var arr = new char[matrix.GetLength(0)][];
 for (int i = 0; i < matrix.GetLength(0); i++)
 {
 arr[i] = new char[matrix.GetLength(1)];
 for (int j = 0; j < matrix.GetLength(1); j++)
 {
 arr[i][j] = matrix[i, j].ToCharArray()[0];
 }
 }

 return arr;
 }
 }
}