LeetCode-in-Java

2257. Count Unguarded Cells in the Grid

Medium

You are given two integers m and n representing a 0-indexed m x n grid. You are also given two 2D integer arrays guards and walls where guards[i] = [rowi, coli] and walls[j] = [rowj, colj] represent the positions of the ith guard and jth wall respectively.

A guard can see every cell in the four cardinal directions (north, east, south, or west) starting from their position unless obstructed by a wall or another guard. A cell is guarded if there is at least one guard that can see it.

Return the number of unoccupied cells that are not guarded.

Example 1:

Input: m = 4, n = 6, guards = [[0,0],[1,1],[2,3]], walls = [[0,1],[2,2],[1,4]]

Output: 7

Explanation: The guarded and unguarded cells are shown in red and green respectively in the above diagram. There are a total of 7 unguarded cells, so we return 7.

Example 2:

Input: m = 3, n = 3, guards = [[1,1]], walls = [[0,1],[1,0],[2,1],[1,2]]

Output: 4

Explanation: The unguarded cells are shown in green in the above diagram. There are a total of 4 unguarded cells, so we return 4.

Constraints:

• 1 <= m, n <= 105
• 2 <= m * n <= 105
• 1 <= guards.length, walls.length <= 5 * 104
• 2 <= guards.length + walls.length <= m * n
• guards[i].length == walls[j].length == 2
• 0 <= rowi, rowj < m
• 0 <= coli, colj < n
• All the positions in guards and walls are unique.

Solution

public class Solution {
    public int countUnguarded(int m, int n, int[][] guards, int[][] walls) {
        char[][] matrix = new char[m][n];
        int result = 0;
        for (int i = 0; i <= guards.length - 1; i++) {
            int guardRow = guards[i][0];
            int guardCol = guards[i][1];
            matrix[guardRow][guardCol] = 'G';
        }
        for (int i = 0; i <= walls.length - 1; i++) {
            int wallRow = walls[i][0];
            int wallCol = walls[i][1];
            matrix[wallRow][wallCol] = 'W';
        }
        for (int i = 0; i <= guards.length - 1; i++) {
            int currentRow = guards[i][0];
            int currentCol = guards[i][1] - 1;
            extracted(matrix, currentRow, currentCol);
            currentRow = guards[i][0];
            currentCol = guards[i][1] + 1;
            extracted(n, matrix, currentRow, currentCol);
            currentRow = guards[i][0] - 1;
            currentCol = guards[i][1];
            extracted1(matrix, currentRow, currentCol);
            currentRow = guards[i][0] + 1;
            currentCol = guards[i][1];
            extracted1(m, matrix, currentRow, currentCol);
        }
        for (int i = 0; i <= m - 1; i++) {
            for (int j = 0; j <= n - 1; j++) {
                if (matrix[i][j] != 'R' && matrix[i][j] != 'G' && matrix[i][j] != 'W') {
                    result++;
                }
            }
        }
        return result;
    }

    private void extracted1(int m, char[][] matrix, int currentRow, int currentCol) {
        while (currentRow <= m - 1) {
            if (matrix[currentRow][currentCol] != 'W' && matrix[currentRow][currentCol] != 'G') {
                matrix[currentRow][currentCol] = 'R';
            } else {
                break;
            }
            currentRow++;
        }
    }

    private void extracted1(char[][] matrix, int currentRow, int currentCol) {
        while (currentRow >= 0) {
            if (matrix[currentRow][currentCol] != 'W' && matrix[currentRow][currentCol] != 'G') {
                matrix[currentRow][currentCol] = 'R';
            } else {
                break;
            }
            currentRow--;
        }
    }

    private void extracted(int n, char[][] matrix, int currentRow, int currentCol) {
        while (currentCol <= n - 1) {
            if (matrix[currentRow][currentCol] != 'W' && matrix[currentRow][currentCol] != 'G') {
                matrix[currentRow][currentCol] = 'R';
            } else {
                break;
            }
            currentCol++;
        }
    }

    private void extracted(char[][] matrix, int currentRow, int currentCol) {
        while (currentCol >= 0) {
            if (matrix[currentRow][currentCol] != 'W' && matrix[currentRow][currentCol] != 'G') {
                matrix[currentRow][currentCol] = 'R';
            } else {
                break;
            }
            currentCol--;
        }
    }
}

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