Given a boolean matrix, update it so that if any cell is true, all the rows and column in that cell are true. - Java Data Structure

Java examples for Data Structure:Matrix

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Description

Given a boolean matrix, update it so that if any cell is true, all the rows and column in that cell are true.

Demo Code

import java.util.Arrays;

public class ZeroMatrix {
    public static void zeroMatrix(boolean[][] matrix) {

        // Verify the input array is nonzero
        if (matrix.length == 0 || matrix[0].length == 0)
            return;

        // Determine whether the first row or first column is true
        boolean rowZero = false, colZero = false;
        for (boolean i : matrix[0]) {
            rowZero |= i;//from   w w  w . j a  v  a 2  s. c  o m
        }
        for (boolean[] i : matrix) {
            colZero |= i[0];
        }

        // For each cell not in the first row/column, if it is true, set the 
        // cell in the first row/same column and first column/same row to be 
        // true
        for (int i = 1; i < matrix.length; i++) {
            for (int j = 1; j < matrix[0].length; j++) {
                if (matrix[i][j]) {
                    matrix[i][0] = true;
                    matrix[0][j] = true;
                }
            }
        }

        // Go through the first column and set each row to true where cell in
        // the first column is true
        for (int i = 1; i < matrix.length; i++) {
            if (matrix[i][0]) {
                for (int j = 1; j < matrix[i].length; j++) {
                    matrix[i][j] = true;
                }
            }
        }

        // Repeat for the rows
        for (int j = 1; j < matrix[0].length; j++) {
            if (matrix[0][j]) {
                for (int i = 1; i < matrix.length; i++) {
                    matrix[i][j] = true;
                }
            }
        }

        // Set first row/column to true if necessary
        if (rowZero) {
            for (int i = 0; i < matrix[0].length; i++) {
                matrix[0][i] = true;
            }
        }

        if (colZero) {
            for (int i = 0; i < matrix.length; i++) {
                matrix[i][0] = true;
            }
        }
    }

    // Sample test cases
    public static void main(String[] args) {
        boolean[][] a = new boolean[][] { { true, false, false },
                { false, false, false }, { false, false, false } };
        zeroMatrix(a);
        assert compare2dArrays(a, new boolean[][] { { true, true, true },
                { true, false, false }, { true, false, false } }) : "First row and first column";

        a = new boolean[][] { { false, false, false },
                { false, false, false }, { false, false, false } };
        zeroMatrix(a);
        assert compare2dArrays(a, new boolean[][] {
                { false, false, false }, { false, false, false },
                { false, false, false } }) : "All false";

    }

    private static boolean compare2dArrays(boolean[][] a, boolean[][] b) {
        if (a.length != b.length)
            return false;
        if (a[0].length != b[0].length)
            return false;

        for (int i = 0; i < a.length; i++) {
            for (int j = 0; j < a[0].length; j++) {
                if (a[i][j] != b[i][j])
                    return false;
            }
        }

        return true;
    }
}

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