Data commit

Task/Truncatable-primes/Go/truncatable-primes.go

@@ -0,0 +1,55 @@
+package main
+
+import "fmt"
+
+func main() {
+    sieve(1e6)
+    if !search(6, 1e6, "left", func(n, pot int) int { return n % pot }) {
+        panic("997?")
+    }
+    if !search(6, 1e6, "right", func(n, _ int) int { return n / 10 }) {
+        panic("7393?")
+    }
+}
+
+var c []bool
+
+func sieve(ss int) {
+    c = make([]bool, ss)
+    c[1] = true
+    for p := 2; ; {
+        p2 := p * p
+        if p2 >= ss {
+            break
+        }
+        for i := p2; i < ss; i += p {
+            c[i] = true
+        }
+        for {
+            p++
+            if !c[p] {
+                break
+            }
+        }
+    }
+}
+
+func search(digits, pot int, s string, truncFunc func(n, pot int) int) bool {
+    n := pot - 1
+    pot /= 10
+smaller:
+    for ; n >= pot; n -= 2 {
+        for tn, tp := n, pot; tp > 0; tp /= 10 {
+            if tn < tp || c[tn] {
+                continue smaller
+            }
+            tn = truncFunc(tn, tp)
+        }
+        fmt.Println("max", s, "truncatable:", n)
+        return true
+    }
+    if digits > 1 {
+        return search(digits-1, pot, s, truncFunc)
+    }
+    return false
+}