Data commit

Task/Prime-triangle/Swift/prime-triangle.swift

@@ -0,0 +1,77 @@
+import Foundation
+
+func isPrime(_ n: Int) -> Bool {
+    guard n > 0 && n < 64 else {
+        return false
+    }
+    return ((UInt64(1) << n) & 0x28208a20a08a28ac) != 0
+}
+
+func primeTriangleRow(_ a: inout [Int], start: Int, length: Int) -> Bool {
+    if length == 2 {
+        return isPrime(a[start] + a[start + 1])
+    }
+    for i in stride(from: 1, to: length - 1, by: 2) {
+        let index = start + i
+        if isPrime(a[start] + a[index]) {
+            a.swapAt(index, start + 1)
+            if primeTriangleRow(&a, start: start + 1, length: length - 1) {
+                return true
+            }
+            a.swapAt(index, start + 1)
+        }
+    }
+    return false
+}
+
+func primeTriangleCount(_ a: inout [Int], start: Int, length: Int) -> Int {
+    var count = 0
+    if length == 2 {
+        if isPrime(a[start] + a[start + 1]) {
+            count += 1
+        }
+    } else {
+        for i in stride(from: 1, to: length - 1, by: 2) {
+            let index = start + i
+            if isPrime(a[start] + a[index]) {
+                a.swapAt(index, start + 1)
+                count += primeTriangleCount(&a, start: start + 1, length: length - 1)
+                a.swapAt(index, start + 1)
+            }
+        }
+    }
+    return count
+}
+
+func printRow(_ a: [Int]) {
+    if a.count == 0 {
+        return
+    }
+    print(String(format: "%2d", a[0]), terminator: "")
+    for x in a[1...] {
+        print(String(format: " %2d", x), terminator: "")
+    }
+    print()
+}
+
+let startTime = CFAbsoluteTimeGetCurrent()
+
+for n in 2...20 {
+    var a = Array(1...n)
+    if primeTriangleRow(&a, start: 0, length: n) {
+        printRow(a)
+    }
+}
+print()
+
+for n in 2...20 {
+    var a = Array(1...n)
+    if n > 2 {
+        print(" ", terminator: "")
+    }
+    print("\(primeTriangleCount(&a, start: 0, length: n))", terminator: "")
+}
+print()
+
+let endTime = CFAbsoluteTimeGetCurrent()
+print("\nElapsed time: \(endTime - startTime) seconds")