SearchA2DMatrix.java

package divide_and_conquer;

/**
 * Created by gouthamvidyapradhan on 09/03/2017.
 * Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:
 * <p>
 * Integers in each row are sorted in ascending from left to right.
 * Integers in each column are sorted in ascending from top to bottom.
 * For example,
 * <p>
 * Consider the following matrix:
 * <p>
 * [
 * [1,   4,  7, 11, 15],
 * [2,   5,  8, 12, 19],
 * [3,   6,  9, 16, 22],
 * [10, 13, 14, 17, 24],
 * [18, 21, 23, 26, 30]
 * ]
 * Given target = 5, return true.
 * <p>
 * Given target = 20, return false.
 */
public class SearchA2DMatrix {
    /**
     * Main method
     *
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception {
        int[][] matrix =
                {
                        {1, 3, 5, 7, 9},     //1, 3, 5, 7, 9
                        {2, 4, 6, 8, 10},     //2, 4, 6, 8, 10
                        {11, 13, 15, 17, 19}, //11, 15, 17, 18, 19
                        {12, 14, 16, 18, 20}, //13, 20, 21, 22, 23
                        {21, 22, 23, 24, 25}  //14, 25, 26, 27, 28
                };

        System.out.println(new SearchA2DMatrix().searchMatrix(matrix, 11));
    }

    private boolean searchMatrix(int[][] matrix, int target) {
        if (matrix.length == 0) return false;
        int M = matrix.length;
        int N = matrix[0].length;
        int r = 0, c = N - 1;
        while (r < M && c >= 0) {
            if (matrix[r][c] == target) return true;
            else if (target < matrix[r][c]) --c;
            else if (target > matrix[r][c]) r++;
        }
        return false;
    }
}