Question

How to check if a matrix columns contain numbers without repetition in Java

Answer 1

import java.util.HashSet;

public class ColumnUniqueNumbers {
    public static boolean columnsHaveUniqueNumbers(int[][] matrix) {
        if (matrix.length == 0 || matrix[0].length == 0) {
            return true;
        }

        int numCols = matrix[0].length;
        for (int j = 0; j < numCols; j++) {
            HashSet<Integer> columnSet = new HashSet<>();

            for (int[] row : matrix) {
                if (!columnSet.add(row[j])) {
                    return false;
                }
            }
        }
        return true;
    }

    public static void main(String[] args) {
        int[][] matrix1 = {
            {1, 4, 7},
            {2, 5, 8},
            {3, 6, 9}
        };

        int[][] matrix2 = {
            {1, 4, 7},
            {2, 4, 8},
            {3, 6, 9}
        };

        System.out.println("Matrix 1 columns have unique numbers: " + columnsHaveUniqueNumbers(matrix1));
        System.out.println("Matrix 2 columns have unique numbers: " + columnsHaveUniqueNumbers(matrix2));
    }
}


/*
run:

Matrix 1 columns have unique numbers: true
Matrix 2 columns have unique numbers: false

*/

 

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