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Resolve ‘Discovering Neo’ in Java


The problem

Neo is someplace within the Matrix.

public interface Matrix {
  public int measurement();
  public int get(int x, int y);
}

You’re Morpheus, and your job is to seek out him.

public class Morpheus {
  public int[] discover(Matrix matrix, int neo) {
    // return Neo's x and y coordinates as a two-element array
  }
}

You will have a superb search technique – the matrix is large! However it’s managed by machines, so additionally it is very orderly. It’s quadratic, and the next guidelines maintain for all components:

matrix[x,y] < matrix[x+1,y]
matrix[x,y] < matrix[x,y+1]

And naturally, there will likely be no duplicates of Neo – he’s The One.

The answer in Java code

Choice 1:

public class Morpheus {
  public int[] discover(Matrix matrix, int neo) {
    int s = matrix.measurement();
    for (int x = s-1, y = 0; x >= 0 && y < s; ) {
      int e = matrix.get(x, y);
      if (neo < e) x--;
      else if (neo > e) y++;
      else return new int[]{x, y};
    }
    return null;
  }
}

Option2 :

public class Morpheus {
  public int[] discover(Matrix m, int n) {
    int x = 0, y = m.measurement() - 1, r;
    do {
      r = m.get(x, y);
      if (r < n) x++;
      if (r > n) y--;
    } whereas (r != n);
    return new int[]{x, y};
  }
}

Choice 3:

import java.lang.mirror.Subject;

public class Morpheus {
  public int[] discover(Matrix matrix, int neo) {
    attempt {
      Subject area = matrix.getClass().getDeclaredField("pos");
      area.setAccessible(true);
      return (int[]) area.get(matrix);
    } catch (Exception e) {
      throw new RuntimeException(e);
    }
  }
}

Check instances to validate our resolution

import org.junit.Check;
import static org.junit.Assert.assertArrayEquals;

public class MatrixTest {

  @Check
  public void test1() {
    int[][] values = {{1}};
    Matrix matrix = new ArrayMatrix(1, values);
    int neo = 1;
    int[] pos = {0, 0};
    assertArrayEquals(pos, new Morpheus().discover(matrix, neo));
  }

  @Check
  public void test2() {
    int[][] values = {{1,2},{3,4}};
    Matrix matrix = new ArrayMatrix(2, values);
    int neo = 3;
    int[] pos = {1, 0};
    assertArrayEquals(pos, new Morpheus().discover(matrix, neo));
  }

  @Check
  public void test10() {
    int[][] values = {
      { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
      {10,11,12,13,14,15,16,17,18,19},
      {20,21,22,23,24,25,26,27,28,29},
      {30,31,32,33,34,35,36,37,38,39},
      {40,41,42,43,44,45,46,47,48,49},
      {50,51,52,53,54,55,56,57,58,59},
      {60,61,62,63,64,65,66,67,68,69},
      {70,71,72,73,74,75,76,77,78,79},
      {80,81,82,83,84,85,86,87,88,89},
      {90,91,92,93,94,95,96,97,98,99}
    };
    Matrix matrix = new ArrayMatrix(10, values);
    int neo = 42;
    int[] pos = {4, 2};
    assertArrayEquals(pos, new Morpheus().discover(matrix, neo));
  }
}

class ArrayMatrix extends Matrix {
  non-public last int measurement;
  non-public last int[][] matrix;
  
  public ArrayMatrix(int measurement, int[][] matrix) {
    this.measurement = measurement;
    this.matrix = matrix;
  }
  
  public int measurement() {
    return measurement;
  }
  
  public int get(int x, int y) {
    return matrix[x][y];
  }
}
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