Ethiopian Multiplication
Little Anny has a lemonade shop, but she wants to go online and sell the lemonade on her own website. At school she learned how to multiply two numbers and she needs you to implement it now. It's a rather curious way of multiplying numbers, so listen up!
To arrive at the final price, you need to double the price and halve the amount of lemonades. Each time you do that sometimes the price turns into funny objects like rubber ducks, tiny pianos, and even a miniature unicorn! This process repeats until there's only one lemonade left. When that happens, the multiplication is done and the final price is calculated.
Anny's Lemonade Shop
Add link to the standalone example. Note with a badge that this example is part of a web development lecture.
Asking the right questions
'How to cut rubber ducks in half' probably is not a question that would be helpful. Don't be afraid to ask obvious questions.
Mental tools
- Name
while- Type
- loop
- Description
Repeat doubling and halving until you're done.
- Name
modulo- Type
- operator
- Description
Determine the remainder of a given number.
- Name
flooring- Type
- math
- Description
After halving, possibly remaining fractions are dropped.
- Name
if- Type
- conditional
- Description
Check whether a number is odd or even.
Solution
function multiply(a, b) {
let result = a % 2 != 0 ? b : 0
while (a > 1) {
a = Math.floor(a / 2)
b = b * 2
if (a % 2 != 0) result += b
}
return result
}
Harder, Better, Faster
Improve on the algorithm by making it faster or have it consume less memory, or some other kind of trick that makes the solution more awesome.
Related challenges
Check out these coding problems. They are similar in some respect.
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