Hacker News Reader

This would be nicer if they rounded benefiting the customer at all times.

Although I don't exactly see how a few pennies can slow down transactions in any significant way. You can get up to one more penny than you would get in quarters. Pennies come in roles >2 as large as quarters.

View on HN

The usual coin-change-making algorithm for X cents in the US is...

(1) pull ⌊X/25⌋ quarters; set X = X%25

(2) pull ⌊X/10⌋ dimes; set X = X%10

(3) pull ⌊X/5⌋ nickles; set X = X%5

(4) pull X pennies

No pennies means there's never a step 4 -- also the only step that might require pulling 4 coins. When dealing with a line of people during the morning coffee rush, fractions of a second count.

It's not the maximum amount of pennies, but the average. Only a handful of prices result in change requiring 3 quarters or 4 dimes, but 40% of prices require 3-4 pennies in change.

Reply on news.ycombinator.com