Extra primes: Difference between revisions
Added Swift solution
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Last 10 extra primes <= 1,000,000,000:
777753773 777755753 777773333 777773753 777775373 777775553 777775577 777777227 777777577 777777773
</pre>
=={{header|Swift}}==
<lang swift>import Foundation
let wheel = [4,2,4,2,4,6,2,6]
func isPrime(_ number: Int) -> Bool {
if number < 2 {
return false
}
if number % 2 == 0 {
return number == 2
}
if number % 3 == 0 {
return number == 3
}
if number % 5 == 0 {
return number == 5
}
var p = 7
while true {
for w in wheel {
if p * p > number {
return true
}
if number % p == 0 {
return false
}
p += w
}
}
}
func nextPrimeDigitNumber(_ number: Int) -> Int {
if number == 0 {
return 2
}
switch number % 10 {
case 2:
return number + 1
case 3, 5:
return number + 2
default:
return 2 + nextPrimeDigitNumber(number/10) * 10
}
}
func digitSum(_ num: Int) -> Int {
var sum = 0
var n = num
while n > 0 {
sum += n % 10
n /= 10
}
return sum
}
func pad(string: String, width: Int) -> String {
if string.count >= width {
return string
}
return String(repeating: " ", count: width - string.count) + string
}
func commatize(_ number: Int) -> String {
let n = NSNumber(value: number)
return NumberFormatter.localizedString(from: n, number: .decimal)
}
let limit1 = 10000
let limit2 = 1000000000
let last = 10
var p = nextPrimeDigitNumber(0)
var n = 0
print("Extra primes less than \(commatize(limit1)):")
while p < limit1 {
if isPrime(digitSum(p)) && isPrime(p) {
n += 1
print(pad(string: commatize(p), width: 5),
terminator: n % 10 == 0 ? "\n" : " ")
}
p = nextPrimeDigitNumber(p)
}
print("\n\nLast \(last) extra primes less than \(commatize(limit2)):")
var extraPrimes = Array(repeating: 0, count: last)
while p < limit2 {
if isPrime(digitSum(p)) && isPrime(p) {
n += 1
extraPrimes[n % last] = p
}
p = nextPrimeDigitNumber(p)
}
for i in stride(from: last - 1, through: 0, by: -1) {
print("\(commatize(n - i)): \(commatize(extraPrimes[(n - i) % last]))")
}</lang>
{{out}}
<pre>
Extra primes less than 10,000:
2 3 5 7 23 223 227 337 353 373
557 577 733 757 773 2,333 2,357 2,377 2,557 2,753
2,777 3,253 3,257 3,323 3,527 3,727 5,233 5,237 5,273 5,323
5,527 7,237 7,253 7,523 7,723 7,727
Last 10 extra primes less than 1,000,000,000:
9,049: 777,753,773
9,050: 777,755,753
9,051: 777,773,333
9,052: 777,773,753
9,053: 777,775,373
9,054: 777,775,553
9,055: 777,775,577
9,056: 777,777,227
9,057: 777,777,577
9,058: 777,777,773
</pre>
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