Intermediate Exercism • elixir

Eliud's Eggs

Challenge Overview

Help Eliud count the number of eggs in her chicken coop by counting the number of 1 bits in a binary representation.

Introduction

Your friend Eliud inherited a farm from her grandma Tigist. Her granny was an inventor and had a tendency to build things in an overly complicated manner. The chicken coop has a digital display showing an encoded number representing the positions of all eggs that could be picked up.

Eliud is asking you to write a program that shows the actual number of eggs in the coop.

The position information encoding is calculated as follows:

Scan the potential egg-laying spots and mark down a 1 for an existing egg or a 0 for an empty spot.
Convert the number from binary to decimal.
Show the result on the display.

Example 1

Seven individual nest boxes arranged in a row whose first, third, fourth and seventh nests each have a single egg.

 _ _ _ _ _ _ _
|E| |E|E| | |E|

Resulting Binary

1011001

 _ _ _ _ _ _ _
|1|0|1|1|0|0|1|

Decimal number on the display

Actual eggs in the coop

Example 2

Seven individual nest boxes arranged in a row where only the fourth nest has an egg.

 _ _ _ _ _ _ _
| | | |E| | | |

Resulting Binary

0001000

 _ _ _ _ _ _ _
|0|0|0|1|0|0|0|

Decimal number on the display

Actual eggs in the coop

Instructions

Your task is to count the number of 1 bits in the binary representation of a number.

Restrictions

Keep your hands off that bit-count functionality provided by your standard library! Solve this one yourself using other basic tools instead.

Source: Exercism elixir/eliuds-eggs