Which pack size is the best value
The same product sits on the shelf in several pack sizes. A price-comparison badge needs the one with the lowest cost per unit.
- Compare price per unit, not sticker price.
- Skip any pack claiming zero or fewer units — that is bad data, not a bargain.
- On a tie, the larger pack wins.
- With nothing worth comparing, return null.
cheapestPack(packs: list<Pack>) → string?
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 cheapestPack(packs []Pack) *string {
}Worked examples
| Call | Result |
|---|---|
cheapestPack([]Pack{Pack{Label: "single", Units: 1, Price: 300}, Pack{Label: "six", Units: 6, Price: 1500}, Pack{Label: "crate", Units: 24, Price: 6200}}) | pStr("six") |
cheapestPack([]Pack{Pack{Label: "a", Units: 2, Price: 200}, Pack{Label: "b", Units: 4, Price: 400}}) | pStr("b") |
cheapestPack([]Pack{Pack{Label: "broken", Units: 0, Price: 100}, Pack{Label: "ok", Units: 3, Price: 900}}) | pStr("ok") |
cheapestPack([]Pack{}) | nil |
Hint
Cross-multiply instead of dividing: a.price * b.units against b.price * a.units keeps it in integers.
Reference solution in Go
func cheapestPack(packs []Pack) *string {
var best *Pack
for i := range packs {
p := &packs[i]
if p.Units <= 0 {
continue
}
if best == nil {
best = p
continue
}
a, b := p.Price*best.Units, best.Price*p.Units
if a < b || (a == b && p.Units > best.Units) {
best = p
}
}
if best == nil {
return nil
}
return &best.Label
}