Data commit

Task/Strong-and-weak-primes/Swift/strong-and-weak-primes.swift

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+import Foundation
+
+class PrimeSieve {
+    var composite: [Bool]
+
+    init(size: Int) {
+        composite = Array(repeating: false, count: size/2)
+        var p = 3
+        while p * p <= size {
+            if !composite[p/2 - 1] {
+                let inc = p * 2
+                var q = p * p
+                while q <= size {
+                    composite[q/2 - 1] = true
+                    q += inc
+                }
+            }
+            p += 2
+        }
+    }
+
+    func isPrime(number: Int) -> Bool {
+        if number < 2 {
+            return false
+        }
+        if (number & 1) == 0 {
+            return number == 2
+        }
+        return !composite[number/2 - 1]
+    }
+}
+
+func commatize(_ number: Int) -> String {
+    let n = NSNumber(value: number)
+    return NumberFormatter.localizedString(from: n, number: .decimal)
+}
+
+let limit1 = 1000000
+let limit2 = 10000000
+
+class PrimeInfo {
+    let maxPrint: Int
+    var count1: Int
+    var count2: Int
+    var primes: [Int]
+
+    init(maxPrint: Int) {
+        self.maxPrint = maxPrint
+        count1 = 0
+        count2 = 0
+        primes = []
+    }
+
+    func addPrime(prime: Int) {
+        count2 += 1
+        if prime < limit1 {
+            count1 += 1
+        }
+        if count2 <= maxPrint {
+            primes.append(prime)
+        }
+    }
+
+    func printInfo(name: String) {
+        print("First \(maxPrint) \(name) primes: \(primes)")
+        print("Number of \(name) primes below \(commatize(limit1)): \(commatize(count1))")
+        print("Number of \(name) primes below \(commatize(limit2)): \(commatize(count2))")
+    }
+}
+
+var strongPrimes = PrimeInfo(maxPrint: 36)
+var weakPrimes = PrimeInfo(maxPrint: 37)
+
+let sieve = PrimeSieve(size: limit2 + 100)
+
+var p1 = 2, p2 = 3, p3 = 5
+while p2 < limit2 {
+    if sieve.isPrime(number: p3) {
+        let diff = p1 + p3 - 2 * p2
+        if diff < 0 {
+            strongPrimes.addPrime(prime: p2)
+        } else if diff > 0 {
+            weakPrimes.addPrime(prime: p2)
+        }
+        p1 = p2
+        p2 = p3
+    }
+    p3 += 2
+}
+
+strongPrimes.printInfo(name: "strong")
+weakPrimes.printInfo(name: "weak")