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to Darts in the Java Track

Published at May 15 2020 · 0 comments
Instructions
Test suite
Solution

Write a function that returns the earned points in a single toss of a Darts game.

Darts is a game where players throw darts to a target.

In our particular instance of the game, the target rewards with 4 different amounts of points, depending on where the dart lands:

  • If the dart lands outside the target, player earns no points (0 points).
  • If the dart lands in the outer circle of the target, player earns 1 point.
  • If the dart lands in the middle circle of the target, player earns 5 points.
  • If the dart lands in the inner circle of the target, player earns 10 points.

The outer circle has a radius of 10 units (This is equivalent to the total radius for the entire target), the middle circle a radius of 5 units, and the inner circle a radius of 1. Of course, they are all centered to the same point (That is, the circles are concentric) defined by the coordinates (0, 0).

Write a function that given a point in the target (defined by its real cartesian coordinates x and y), returns the correct amount earned by a dart landing in that point.

Setup

Go through the setup instructions for Java to install the necessary dependencies:

https://exercism.io/tracks/java/installation

Running the tests

You can run all the tests for an exercise by entering the following in your terminal:

$ gradle test

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by removing the @Ignore("Remove to run test") annotation.

Source

Inspired by an exercise created by a professor Della Paolera in Argentina

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

DartsTest.java

import org.junit.Ignore;
import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class DartsTest {

    @Test
    public void missedTarget() {
        Darts darts = new Darts(-9, 9);
        assertEquals(0, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void onTheOuterCircle() {
        Darts darts = new Darts(0, 10);
        assertEquals(1, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void onTheMiddleCircle() {
        Darts darts = new Darts(-5, 0);
        assertEquals(5, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void onTheInnerCircle() {
        Darts darts = new Darts(0, -1);
        assertEquals(10, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void exactlyOnCentre() {
        Darts darts = new Darts(0, 0);
        assertEquals(10, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void nearTheCentre() {
        Darts darts = new Darts(-0.1, -0.1);
        assertEquals(10, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void justWithinTheInnerCircle() {
        Darts darts = new Darts(0.7, 0.7);
        assertEquals(10, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void justOutsideTheInnerCircle() {
        Darts darts = new Darts(0.8, -0.8);
        assertEquals(5, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void justWithinTheMiddleCirlce() {
        Darts darts = new Darts(-3.5, 3.5);
        assertEquals(5, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void justOutsideTheMiddleCircle() {
        Darts darts = new Darts(-3.6, -3.6);
        assertEquals(1, darts.score());
    }


    @Ignore("Remove to run test")
    @Test
    public void justWithinTheOuterCirlce() {
        Darts darts = new Darts(-7.0, 7.0);
        assertEquals(1, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void justOutsideTheOuterCircle() {
        Darts darts = new Darts(7.1, -7.1);
        assertEquals(0, darts.score());
    }

    @Ignore("Remove to run test")
    @Test
    public void asymmetricPositionBetweenTheInnerAndMiddleCircles() {
        Darts darts = new Darts(0.5, -4);
        assertEquals(5, darts.score());
    }

}
class Darts {

	private static final int RADIUS_OF_INNER_CIRCLE = 1;
	private static final int RADIUS_OF_MIDDLE_CIRCLE = 5;
	private static final int RADIUS_OF_OUTER_CIRCLE = 10;

	private final double x;
	private final double y;

    Darts(double x, double y) {
		this.x = x;
		this.y = y;
	}

    int score() {
		if(isInsideInnerCircle()) {
			return 10;
		}
		if(isInsideMiddleCircle()) {
			return 5;
		}
		if(isInsideOutserCircle()) {
			return 1;
		}
		return 0;
	}

	boolean isInsideInnerCircle() {
		return distanceToOrigin() <= RADIUS_OF_INNER_CIRCLE;
	}

	boolean isInsideMiddleCircle() {
		return distanceToOrigin() <= RADIUS_OF_MIDDLE_CIRCLE;
	}

	boolean isInsideOutserCircle() {
		return distanceToOrigin() <= RADIUS_OF_OUTER_CIRCLE;
	}

	double distanceToOrigin() {
		return Math.sqrt(Math.pow(this.x, 2) + Math.pow(y, 2));
	}

}

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