Week-on-week price change
A pricing dashboard shows how far each item moved since last week, as a percentage.
- Rounded to one decimal place.
- A previous price of zero has no meaningful percentage: return 0.
- A drop is negative.
percentChange(before: int, after: int) → float
Go needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
func percentChange(before int, after int) float64 {
}Worked examples
| Call | Result |
|---|---|
percentChange(100, 125) | 25.0 |
percentChange(200, 150) | -25.0 |
percentChange(300, 310) | 3.3 |
percentChange(100, 100) | 0.0 |
Hint
difference / before * 100, then round to one decimal by multiplying by 10, rounding, and dividing back.
Reference solution in Go
func percentChange(before int, after int) float64 {
if before == 0 {
return 0
}
pct := float64(after-before) * 100 / float64(before)
return math.Round(pct*10) / 10
}