Data commit

Task/Vampire-number/Go/vampire-number.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+    "fmt"
+    "math"
+)
+
+func max(a, b uint64) uint64 {
+    if a > b {
+        return a
+    }
+    return b
+}
+
+func min(a, b uint64) uint64 {
+    if a < b {
+        return a
+    }
+    return b
+}
+
+func ndigits(x uint64) (n int) {
+    for ; x > 0; x /= 10 {
+        n++
+    }
+    return
+}
+
+func dtally(x uint64) (t uint64) {
+    for ; x > 0; x /= 10 {
+        t += 1 << (x % 10 * 6)
+    }
+    return
+}
+
+var tens [20]uint64
+
+func init() {
+    tens[0] = 1
+    for i := 1; i < 20; i++ {
+        tens[i] = tens[i-1] * 10
+    }
+}
+
+func fangs(x uint64) (f []uint64) {
+    nd := ndigits(x)
+    if nd&1 == 1 {
+        return
+    }
+    nd /= 2
+    lo := max(tens[nd-1], (x+tens[nd]-2)/(tens[nd]-1))
+    hi := min(x/lo, uint64(math.Sqrt(float64(x))))
+    t := dtally(x)
+    for a := lo; a <= hi; a++ {
+        b := x / a
+        if a*b == x &&
+            (a%10 > 0 || b%10 > 0) &&
+            t == dtally(a)+dtally(b) {
+            f = append(f, a)
+        }
+    }
+    return
+}
+
+func showFangs(x uint64, f []uint64) {
+    fmt.Print(x)
+    if len(f) > 1 {
+        fmt.Println()
+    }
+    for _, a := range f {
+        fmt.Println(" =", a, "×", x/a)
+    }
+}
+
+func main() {
+    for x, n := uint64(1), 0; n < 26; x++ {
+        if f := fangs(x); len(f) > 0 {
+            n++
+            fmt.Printf("%2d: ", n)
+            showFangs(x, f)
+        }
+    }
+    fmt.Println()
+    for _, x := range []uint64{16758243290880, 24959017348650, 14593825548650} {
+        if f := fangs(x); len(f) > 0 {
+            showFangs(x, f)
+        } else {
+            fmt.Println(x, "is not vampiric")
+        }
+    }
+}