 artemkorsakov's solution

to Armstrong Numbers in the Java Track

Published at Jan 29 2019 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

An Armstrong number is a number that is the sum of its own digits each raised to the power of the number of digits.

For example:

• 9 is an Armstrong number, because 9 = 9^1 = 9
• 10 is not an Armstrong number, because 10 != 1^2 + 0^2 = 1
• 153 is an Armstrong number, because: 153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153
• 154 is not an Armstrong number, because: 154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190

Write some code to determine whether a number is an Armstrong number.

Java Tips

For more help on how to solve this exercise, please refer to the tutorial provided as part of the hello world exercise: TUTORIAL.md

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ArmstrongNumbersTest.java

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

import static org.junit.Assert.assertTrue;
import static org.junit.Assert.assertFalse;

public class ArmstrongNumbersTest {

private ArmstrongNumbers armstrongNumbers;

@Before
public void setup() {
armstrongNumbers = new ArmstrongNumbers();
}

@Test
public void singleDigitsAreArmstrongNumbers() {
int input = 5;

assertTrue(armstrongNumbers.isArmstrongNumber(input));
}

@Ignore("Remove to run test")
@Test
public void noTwoDigitArmstrongNumbers() {
int input = 10;

assertFalse(armstrongNumbers.isArmstrongNumber(input));
}

@Ignore("Remove to run test")
@Test
public void threeDigitNumberIsArmstrongNumber() {
int input = 153;

assertTrue(armstrongNumbers.isArmstrongNumber(input));
}

@Ignore("Remove to run test")
@Test
public void threeDigitNumberIsNotArmstrongNumber() {
int input = 100;

assertFalse(armstrongNumbers.isArmstrongNumber(input));
}

@Ignore("Remove to run test")
@Test
public void fourDigitNumberIsArmstrongNumber() {
int input = 9474;

assertTrue(armstrongNumbers.isArmstrongNumber(input));
}

@Ignore("Remove to run test")
@Test
public void fourDigitNumberIsNotArmstrongNumber() {
int input = 9475;

assertFalse(armstrongNumbers.isArmstrongNumber(input));
}

@Ignore("Remove to run test")
@Test
public void sevenDigitNumberIsArmstrongNumber() {
int input = 9926315;

assertTrue(armstrongNumbers.isArmstrongNumber(input));
}

@Ignore("Remove to run test")
@Test
public void sevenDigitNumberIsNotArmstrongNumber() {
int input = 9926314;

assertFalse(armstrongNumbers.isArmstrongNumber(input));
}

}
import java.util.Arrays;

class ArmstrongNumbers {

boolean isArmstrongNumber(int numberToCheck) {
String[] nums = String.valueOf(numberToCheck).split("");
return (numberToCheck > 0) && (Arrays.stream(nums).mapToInt(n -> (int) Math.pow(Integer.parseInt(n), nums.length)).sum() == numberToCheck);
}

}