func process(p Problems.Problem) {
daftlog.Printf("Problem %d: %s", p.GetID(), p.GetTitle())
p.CalculateAnswer()
daftlog.Printf("Answer %d: %s", p.GetID(), p.GetAnswer())
if p.IsAnswerVerified() {
daftlog.Printf("Project Euler has verified answer %d as correct.", p.GetID())
}
}
func (p3 *problem3) CalculateAnswer() {
const BaseNumber = 600851475143
var largestPossiblePrimeFactor = uint(math.Sqrt(BaseNumber)) // largest factor of a number is its square root.
// A prime is never even, find the largest odd to start on.
if math.Mod(float64(largestPossiblePrimeFactor), 2) == 0 {
largestPossiblePrimeFactor -= 1
}
daftlog.Printf("Largest possble odd factor of %d = %d", BaseNumber, largestPossiblePrimeFactor)
var primeNotFound = true
for primeNotFound {
if math.Mod(BaseNumber, float64(largestPossiblePrimeFactor)) == 0 { // found an odd factor.
var resultOfPrimeTest string
if isOddPrime(float64(largestPossiblePrimeFactor)) { // is this odd factor a prime?
resultOfPrimeTest = fmt.Sprintf("and %d is a prime!", largestPossiblePrimeFactor)
primeNotFound = false // signal that that we're done searching.
} else {
resultOfPrimeTest = fmt.Sprintf("but %d is not a prime!", largestPossiblePrimeFactor)
}
daftlog.Printf("Found odd factor at %d, %s", largestPossiblePrimeFactor, resultOfPrimeTest)
}
if primeNotFound {
largestPossiblePrimeFactor -= 2 // skip to next smaller odd number as possible factor.
}
}
p3.answer = fmt.Sprintf("%d", largestPossiblePrimeFactor)
p3.answerVerified = true
}
func main() {
var args = new(cmdline.Arguments)
args.Process()
daftlog.SetFormat(daftlog.FormatTimeOnly)
daftlog.Print(cmdline.GetVersionString())
daftlog.Print("Project Euler via Go, (c) 2015, Lindsay Bradford.")
daftlog.Printf(
"Problems Implemented: (%d/%d)",
config.LastImplementedEulerProblemID,
config.MaxEulerProblemID,
)
daftlog.Print("")
process(
Problems.BuildProblem(args.Problem),
)
}
