Java/Ch 01. Arrays and Strings/Q1_08_Zero_Matrix/QuestionB.java

[GaiNingMorris]

No need to separate first column with the rest columns to check if there is zero.

public class QuestionB {

    public static void main(String[] args) {
        int[][] matrix = { { 1, 0, 3, 4 }, { 5, 0, 7, 8 }, { 9, 10, 11, 12 } };
        setZeros(matrix);

        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println();
        }
    }

    public static void nullifyRow(int[][] matrix, int row) {
        for (int j = 0; j < matrix[0].length; j++) {
            matrix[row][j] = 0;
        }
    }

    public static void nullifyColumn(int[][] matrix, int col) {
        for (int i = 0; i < matrix.length; i++) {
            matrix[i][col] = 0;
        }
    }

    public static void setZeros(int[][] matrix) {
        boolean rowHasZero = false;

        // Check if first row has a zero
        for (int j = 0; j < matrix[0].length; j++) {
            if (matrix[0][j] == 0) {
                rowHasZero = true;
                break;
            }
        }

        // Check for zeros in the rest of the array
        for (int i = 1; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                if (matrix[i][j] == 0) {
                    matrix[i][0] = 0;
                    matrix[0][j] = 0;
                }
            }
        }

        // Nullify rows based on values in first column
        for (int i = 1; i < matrix.length; i++) {
            if (matrix[i][0] == 0) {
                nullifyRow(matrix, i);
            }
        }

        // Nullify columns based on values in first row
        for (int j = 0; j < matrix[0].length; j++) {
            if (matrix[0][j] == 0) {
                nullifyColumn(matrix, j);
            }
        }

        // Nullify first row
        if (rowHasZero) {
            nullifyRow(matrix, 0);
        }
    }
}