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p77.go
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p77.go
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package main
import (
"fmt"
"math"
"time"
)
func IsPrime(prime []int, x int) bool {
bound := int(math.Sqrt(float64(x)))
if x%bound == 0 {
return false
}
for _, p := range prime {
if p > bound {
return true
}
if x%p == 0 {
return false
}
}
return true
}
func Comb(prime []int, x, y int) int {
sum := 0
if y > x {
y = x
}
for _, p := range prime {
if p > y {
break
} else {
if x-p == 0 {
sum++
} else {
sum += Comb(prime, x-p, p)
}
}
}
return sum
}
func main() {
start := time.Now()
prime, maxP := []int{2, 3, 5}, 5
for {
maxP += 2
if IsPrime(prime, maxP) {
prime = append(prime, maxP)
}
if Comb(prime, maxP-1, maxP-2) > 5000 {
fmt.Println(maxP - 1)
break
}
if Comb(prime, maxP, maxP-1) > 5000 {
fmt.Println(maxP)
break
}
}
elapsed := time.Since(start)
fmt.Println("Elasped:", elapsed)
}