Data commit

Task/Truncatable-primes/Swift/truncatable-primes.swift

@@ -0,0 +1,69 @@
+func isPrime(_ n: Int) -> Bool {
+    if n < 2 {
+        return false
+    }
+    if n % 2 == 0 {
+        return n == 2
+    }
+    if n % 3 == 0 {
+        return n == 3
+    }
+    var p = 5
+    while p * p <= n {
+        if n % p == 0 {
+            return false
+        }
+        p += 2
+        if n % p == 0 {
+            return false
+        }
+        p += 4
+    }
+    return true
+}
+
+func isLeftTruncatable(_ p: Int) -> Bool {
+    var n = 10
+    var q = p
+    while p > n {
+        if !isPrime(p % n) || q == p % n {
+            return false
+        }
+        q = p % n
+        n *= 10
+    }
+    return true
+}
+
+func isRightTruncatable(_ p: Int) -> Bool {
+    var q = p / 10
+    while q > 0 {
+        if !isPrime(q) {
+            return false
+        }
+        q /= 10
+    }
+    return true
+}
+
+let limit = 1000000
+var largestLeft = 0
+var largestRight = 0
+var p = limit
+while p >= 2 {
+    if isPrime(p) && isLeftTruncatable(p) {
+        largestLeft = p
+        break
+    }
+    p -= 1
+}
+print("Largest left truncatable prime is \(largestLeft)")
+p = limit
+while p >= 2 {
+    if isPrime(p) && isRightTruncatable(p) {
+        largestRight = p
+        break
+    }
+    p -= 1
+}
+print("Largest right truncatable prime is \(largestRight)")