codewars/go/kyu7/growth_of_a_population/k.go

package kata

import "math"

// percent is no predivided by 100: 2% is passed as 2.
func NextPop(pn int, percent float64, aug int) int {
	next := int(math.Floor(float64(pn) * (1 + percent/100))) + aug
	return next
}

// Cannot use the power formula because of integer truncation at each step.
func PopN(p0 int, percent float64, aug int, n int) int {
	pn := p0
	for i := 0; i < n; i++ {
		pn = NextPop(pn, percent, aug)
	}
	return pn
}

func NbYear(p0 int, percent float64, aug int, p int) int {
	pn := p0
	year := 0
	// Support population decrease caused by invalid parameters.
	for year = 0; pn < p && pn >= 0; year++ {
		pn = NextPop(pn, percent, aug)
	}
	return year
}