Avatar of bkhl

bkhl's solution

to Armstrong Numbers in the Bash Track

Published at Jan 05 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.

Run the tests with:

bats armstrong_numbers_test.sh

After the first test(s) pass, continue by commenting out or removing the skip annotations prepending other tests.

Source

Wikipedia https://en.wikipedia.org/wiki/Narcissistic_number

External utilities

Bash is a language to write scripts that works closely with various system utilities, like sed, awk, date and even other programming languages, like Python. This track does not restrict the usage of these utilities, and as long as your solution is portable between systems and does not require installing third party applications, feel free to use them to solve the exercise.

For an extra challenge, if you would like to have a better understanding of the language, try to re-implement the solution in pure Bash, without using any external tools.

Submitting Incomplete Solutions

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

armstrong_numbers_test.sh

#!/usr/bin/env bats

@test 'Single digits are Armstrong numbers' {
  # skip
  run bash armstrong_numbers.sh 5

  [ "$status" -eq 0 ]
  [ "$output" = "true" ]
}

@test 'There are no two digit Armstrong numbers' {
  skip
  run bash armstrong_numbers.sh 10

  [ "$status" -eq 1 ]
  [ "$output" = "false" ]
}

@test 'A three digit number that is an Armstrong number' {
  skip
  run bash armstrong_numbers.sh 153

  [ "$status" -eq 0 ]
  [ "$output" = "true" ]
}

@test 'A three digit number that is not an Armstrong number' {
  skip
  run bash armstrong_numbers.sh 100

  [ "$status" -eq 1 ]
  [ "$output" = "false" ]
}

@test 'A four digit number that is an Armstrong number' {
  skip
  run bash armstrong_numbers.sh 9474

  [ "$status" -eq 0 ]
  [ "$output" = "true" ]
}

@test 'A four digit number that is not an Armstrong number' {
  skip
  run bash armstrong_numbers.sh 9475

  [ "$status" -eq 1 ]
  [ "$output" = "false" ]
}

@test 'A seven digit number that is an Armstrong number' {
  skip
  run bash armstrong_numbers.sh 9926315

  [ "$status" -eq 0 ]
  [ "$output" = "true" ]
}

@test 'A seven digit number that is not an Armstrong number' {
  skip
  run bash armstrong_numbers.sh 9926314

  [ "$status" -eq 1 ]
  [ "$output" = "false" ]
}
#!/bin/bash

# Check if input is an armstrong number. Print "true" or "false" and
# return with success or failure code accordingly.
validate() {
    number="$1"

    sum=0
    digit_count=${#number}
    for (( i = 0; i < digit_count; i++ )); do
        sum=$(( sum + ${number:$i:1} ** digit_count))
    done

    if [[ "$sum" == "$number" ]]; then
        echo true
    else
        echo false
        return 1
    fi
}

validate "$*" || exit 1

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?