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Count positions in a chessboard that can be visited by the Queen which are not visited by the King
  • Last Updated : 28 Apr, 2021

Given two integers N and M denoting the dimensions of a chessboard, and two integers X and Y denoting the King’s position, i.e. the cell (X, Y). The task is to find the number of cells the Queen can visit that are not visited by the King if it gets replaced by the King. The King visits all his adjacent cells and the Queen can move diagonally, horizontally, and vertically.

Examples:

Input: N = 8, M = 8, X = 1, Y = 1
Output: 18
Explanation:
Below is the image to show the movement of King and Queen: 
 

 



Suppose K represents King and * represents cells visited by the king and Q represents Queen and # represent the cells visited by the queen.
So, the total squares can be visited by the queen is 18.

Input: N = 2, M = 1, X = 1, Y = 1
Output: 0

Approach: The idea is to first find the total number of positions that the Queen can visit. Then find the total number of positions that the King can visit. The number of cells that can only be visited by the Queen will be the number of cells the King can visit subtracted from the number of cells the Queen can visit. Follow the below steps to solve the problem:

  • Initialize queenMoves by 0 and calculate the total moves of the Queen as follows:

If N – X > 0 and M – Y > 0, queenMoves = queenMoves + min(N – X, M – Y) 
If X – 1 > 0 and Y – 1 > 0, queenMoves = queenMoves + min(Y – 1, X – 1) 
If X – 1 > 0 and M – Y > 0, queenMoves = queenMoves  + min(X – 1, M – Y) 
If N – X > 0 and Y – 1 > 0, queenMoves = queenMoves + min(N – X, Y – 1) 
At last, add the answer for horizontal and vertical movements as queenMoves = queenMoves + (N – 1) + (M – 1)

  • Initialize kingMoves as 0 and calculate King’s moves as follows:

If X + 1 <= N,  kingMoves = kingMoves + 1
If X – 1 > 0,  kingMoves = kingMoves + 1
If Y + 1 <= M,  kingMoves = kingMoves + 1
If Y – 1 > 0,  kingMoves = kingMoves + 1
If X + 1 <= N and Y + 1 <= M,  kingMoves = kingMoves + 1
If X + 1 <= N and Y – 1 > 0,  kingMoves = kingMoves + 1
If X – 1 > 0 and Y – 1 > 0,  kingMoves = kingMoves + 1
If X – 1 > 0 and Y + 1 <= M,  kingMoves = kingMoves + 1

  • Print the absolute difference between the Queen’s and King’s calculated in the above steps as the result.

Below is the implementation of the above approach:

C++




// C++ program for the above approach
#include <iostream>
using namespace std;
 
// Function to print the number of cells
// only visited by the queen
int Moves_Calculator(int x, int y,
                     int row, int col)
{
     
    // Find all the moves
    int total_moves = 0;
     
    // Find all moves for x + 1, y + 1
    if ((row - x) > 0 && (col - y) > 0)
        total_moves += min((row - x),
                           (col - y));
 
    // Find all moves for x - 1, y - 1
    if ((y - 1) > 0 && (x - 1) > 0)
        total_moves += min((y - 1),
                           (x - 1));
 
    // Find all moves for x - 1, y + 1
    if ((x - 1) > 0 && (col - y) > 0)
        total_moves += min((x - 1),
                         (col - y));
 
    // Find all moves for x + 1, y - 1
    if ((row - x) > 0 && (y - 1) > 0)
        total_moves += min((row - x),
                             (y - 1));
 
    total_moves += (row - 1) + (col - 1);
 
    // Find all squares visited by King
    // x + 1, in same row
    int king_moves = 0;
     
    if (x + 1 <= row)
        king_moves += 1;
 
    // x - 1, in same row
    if (x - 1 > 0)
        king_moves += 1;
 
    // y + 1, in same column
    if (y + 1 <= col)
        king_moves += 1;
 
    // y - 1, in same column
    if (y - 1 > 0)
        king_moves += 1;
 
    if (x + 1 <= row && y + 1 <= col)
        king_moves += 1;
 
    if (x + 1 <= row && y - 1 > 0)
        king_moves += 1;
 
    if (x - 1 > 0 && y - 1 > 0)
        king_moves += 1;
 
    if (x - 1 > 0 && y + 1 <= col)
        king_moves += 1;
 
    // Return answer
    return total_moves - king_moves;
}
 
// Driver Code
int main()
{
     
    // Dimension of Board
    int n = 8, m = 8;
     
    // Position of Cell
    int x = 1, y = 1;
     
    // Function Call
    cout << (Moves_Calculator(x, y, m, n));
    return 0;
}
 
// This code is contributed by akhilsaini

Java




// Java program for the above approach
import java.io.*;
 
class GFG{
 
// Function to print the number of cells
// only visited by the queen
static int Moves_Calculator(int x, int y,
                            int row, int col)
{
     
    // Find all the moves
    int total_moves = 0;
 
    // Find all moves for x + 1, y + 1
    if ((row - x) > 0 && (col - y) > 0)
        total_moves += Math.min((row - x),
                                (col - y));
 
    // Find all moves for x - 1, y - 1
    if ((y - 1) > 0 && (x - 1) > 0)
        total_moves += Math.min((y - 1),
                                (x - 1));
 
    // Find all moves for x - 1, y + 1
    if ((x - 1) > 0 && (col - y) > 0)
        total_moves += Math.min((x - 1),
                              (col - y));
 
    // Find all moves for x + 1, y - 1
    if ((row - x) > 0 && (y - 1) > 0)
        total_moves += Math.min((row - x),
                                  (y - 1));
 
    total_moves += (row - 1) + (col - 1);
 
    // Find all squares visited by King
    // x + 1, in same row
    int king_moves = 0;
    if (x + 1 <= row)
        king_moves += 1;
 
    // x - 1, in same row
    if (x - 1 > 0)
        king_moves += 1;
 
    // y + 1, in same column
    if (y + 1 <= col)
        king_moves += 1;
 
    // y - 1, in same column
    if (y - 1 > 0)
        king_moves += 1;
 
    if (x + 1 <= row && y + 1 <= col)
        king_moves += 1;
 
    if (x + 1 <= row && y - 1 > 0)
        king_moves += 1;
 
    if (x - 1 > 0 && y - 1 > 0)
        king_moves += 1;
 
    if (x - 1 > 0 && y + 1 <= col)
        king_moves += 1;
 
    // Return answer
    return total_moves - king_moves;
}
 
// Driver Code
public static void main(String[] args)
{
     
    // Dimension of Board
    int n = 8, m = 8;
 
    // Position of Cell
    int x = 1, y = 1;
 
    // Function Call
    System.out.println(Moves_Calculator(x, y, m, n));
}
}
 
// This code is contributed by akhilsaini

Python3




# Python3 program for the above approach
 
# Function to print the number of cells
# only visited by the queen
def Moves_Calculator(x, y, row, col):
 
    # Find all the moves
    total_moves = 0
     
    # Find all moves for x + 1, y + 1
    if (row - x) > 0 and (col - y) > 0:
        total_moves += min((row - x), (col - y))
 
    # Find all moves for x - 1, y - 1
    if (y - 1) > 0 and (x - 1) > 0:
        total_moves += min((y - 1), (x - 1))
 
    # Find all moves for x - 1, y + 1
    if (x - 1) > 0 and (col - y) > 0:
        total_moves += min((x - 1), (col - y))
 
    # Find all moves for x + 1, y - 1
    if (row - x) > 0 and (y - 1) > 0:
        total_moves += min((row - x), (y - 1))
 
    total_moves += (row - 1) + (col - 1)
 
    # Find all squares visited by King
    # x + 1, in same row
    king_moves = 0
    if x + 1 <= m:
        king_moves += 1
 
    # x - 1, in same row
    if x - 1 > 0:
        king_moves += 1
 
    # y + 1, in same column
    if y + 1 <= n:
        king_moves += 1
 
    # y - 1, in same column
    if y - 1 > 0:
        king_moves += 1
 
    if x + 1 <= m and y + 1 <= n:
        king_moves += 1
 
    if x + 1 <= m and y - 1 > 0:
        king_moves += 1
 
    if x - 1 > 0 and y - 1 > 0:
        king_moves += 1
 
    if x - 1 > 0 and y + 1 <= n:
        king_moves += 1
 
    # Return answer
    return total_moves - king_moves
 
 
# Driver Code
if __name__ == '__main__':
 
    # Dimension of Board
    n, m = 8, 8
     
    # Position of Cell
    x, y = 1, 1
     
    # Function Call
    print(Moves_Calculator(x, y, m, n))

C#




// C# program for the above approach
using System;
 
class GFG{
 
// Function to print the number of cells
// only visited by the queen
static int Moves_Calculator(int x, int y,
                            int row, int col)
{
     
    // Find all the moves
    int total_moves = 0;
 
    // Find all moves for x + 1, y + 1
    if ((row - x) > 0 && (col - y) > 0)
        total_moves += Math.Min((row - x),
                                (col - y));
 
    // Find all moves for x - 1, y - 1
    if ((y - 1) > 0 && (x - 1) > 0)
        total_moves += Math.Min((y - 1),
                                (x - 1));
 
    // Find all moves for x - 1, y + 1
    if ((x - 1) > 0 && (col - y) > 0)
        total_moves += Math.Min((x - 1),
                              (col - y));
 
    // Find all moves for x + 1, y - 1
    if ((row - x) > 0 && (y - 1) > 0)
        total_moves += Math.Min((row - x),
                                  (y - 1));
 
    total_moves += (row - 1) + (col - 1);
 
    // Find all squares visited by King
    // x + 1, in same row
    int king_moves = 0;
    if (x + 1 <= row)
        king_moves += 1;
 
    // x - 1, in same row
    if (x - 1 > 0)
        king_moves += 1;
 
    // y + 1, in same column
    if (y + 1 <= col)
        king_moves += 1;
 
    // y - 1, in same column
    if (y - 1 > 0)
        king_moves += 1;
 
    if (x + 1 <= row && y + 1 <= col)
        king_moves += 1;
 
    if (x + 1 <= row && y - 1 > 0)
        king_moves += 1;
 
    if (x - 1 > 0 && y - 1 > 0)
        king_moves += 1;
 
    if (x - 1 > 0 && y + 1 <= col)
        king_moves += 1;
 
    // Return answer
    return total_moves - king_moves;
}
 
// Driver Code
public static void Main()
{
 
    // Dimension of Board
    int n = 8, m = 8;
 
    // Position of Cell
    int x = 1, y = 1;
 
    // Function Call
    Console.WriteLine(Moves_Calculator(x, y, m, n));
}
}
 
// This code is contributed by akhilsaini

Javascript




<script>
 
// Javascript program for the above approach
 
// Function to prlet the number of cells
// only visited by the queen
function Moves_Calculator(x, y, row, col)
{
      
    // Find all the moves
    let total_moves = 0;
  
    // Find all moves for x + 1, y + 1
    if ((row - x) > 0 && (col - y) > 0)
        total_moves += Math.min((row - x),
                                (col - y));
  
    // Find all moves for x - 1, y - 1
    if ((y - 1) > 0 && (x - 1) > 0)
        total_moves += Math.min((y - 1),
                                (x - 1));
  
    // Find all moves for x - 1, y + 1
    if ((x - 1) > 0 && (col - y) > 0)
        total_moves += Math.min((x - 1),
                              (col - y));
  
    // Find all moves for x + 1, y - 1
    if ((row - x) > 0 && (y - 1) > 0)
        total_moves += Math.min((row - x),
                                  (y - 1));
  
    total_moves += (row - 1) + (col - 1);
  
    // Find all squares visited by King
    // x + 1, in same row
    let king_moves = 0;
    if (x + 1 <= row)
        king_moves += 1;
  
    // x - 1, in same row
    if (x - 1 > 0)
        king_moves += 1;
  
    // y + 1, in same column
    if (y + 1 <= col)
        king_moves += 1;
  
    // y - 1, in same column
    if (y - 1 > 0)
        king_moves += 1;
  
    if (x + 1 <= row && y + 1 <= col)
        king_moves += 1;
  
    if (x + 1 <= row && y - 1 > 0)
        king_moves += 1;
  
    if (x - 1 > 0 && y - 1 > 0)
        king_moves += 1;
  
    if (x - 1 > 0 && y + 1 <= col)
        king_moves += 1;
  
    // Return answer
    return total_moves - king_moves;
}
 
// Driver code
 
// Dimension of Board
let n = 8, m = 8;
 
// Position of Cell
let x = 1, y = 1;
 
// Function Call
document.write(Moves_Calculator(x, y, m, n));
 
// This code is contributed by splevel62  
 
</script>
Output: 
18

 

Time Complexity: O(1)
Auxiliary Space: O(1)

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