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to Trinary in the Java Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Convert a trinary number, represented as a string (e.g. '102012'), to its decimal equivalent using first principles.

The program should consider strings specifying an invalid trinary as the value 0.

Trinary numbers contain three symbols: 0, 1, and 2.

The last place in a trinary number is the 1's place. The second to last is the 3's place, the third to last is the 9's place, etc.

# "102012"
    1       0       2       0       1       2    # the number
1*3^5 + 0*3^4 + 2*3^3 + 0*3^2 + 1*3^1 + 2*3^0    # the value
  243 +     0 +    54 +     0 +     3 +     2 =  302

If your language provides a method in the standard library to perform the conversion, pretend it doesn't exist and implement it yourself.

Running the tests

You can run all the tests for an exercise by entering

$ gradle test

in your terminal.

Source

All of Computer Science http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-

Submitting Incomplete Solutions

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

TrinaryTest.java

import static org.junit.Assert.assertEquals;

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

public class TrinaryTest {

    @Test
    public void testNonTrinaryCharacterIsZero() {
        assertEquals(0, Trinary.toDecimal("-"));
    }

    @Ignore
    @Test
    public void testNonTrinaryNumberIsZero() {
        assertEquals(0, Trinary.toDecimal("3"));
    }

    @Ignore
    @Test
    public void testTrinaryWithNonTrinaryIsZero() {
        assertEquals(0, Trinary.toDecimal("102-12"));
    }

    @Ignore
    @Test
    public void testTrinary() {
        assertEquals(302, Trinary.toDecimal("102012"));
    }
}
public class Trinary {

  private static int RADIX = 3;

  public static int toDecimal(String input) {
    if (!input.matches("[012]+")) { return 0; }
    return computeTrinary(input);

  }

  private static int computeTrinary(String input) {
    int result = 0;
    int pwr = 1;

    for (int i = input.length() - 1; i >= 0; i--, pwr *= RADIX) {
      int currDigit = Character.digit(input.charAt(i), RADIX);
      result += currDigit * pwr;
    }

    return result;
  }
}

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