Initial data commit

Task/Negative-base-numbers/Go/negative-base-numbers.go

@@ -0,0 +1,74 @@
+package main
+
+import (
+    "fmt"
+    "log"
+    "strings"
+)
+
+const digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+func reverse(bs []byte) []byte {
+    for i, j := 0, len(bs)-1; i < len(bs)/2; i, j = i+1, j-1 {
+        bs[i], bs[j] = bs[j], bs[i]
+    }
+    return bs
+}
+
+func encodeNegBase(n, b int64) (string, error) {
+    if b < -62 || b > -1 {
+        return "", fmt.Errorf("base must be between -62 and -1 inclusive")
+    }
+    if n == 0 {
+        return "0", nil
+    }
+    var out []byte
+    for n != 0 {
+        rem := n % b
+        n /= b
+        if rem < 0 {
+            n++
+            rem -= b
+        }
+        out = append(out, digits[int(rem)])
+    }
+    reverse(out)
+    return string(out), nil
+}
+
+func decodeNegBase(ns string, b int64) (int64, error) {
+    if b < -62 || b > -1 {
+        return 0, fmt.Errorf("base must be between -62 and -1 inclusive")
+    }
+    if ns == "0" {
+        return 0, nil
+    }
+    total := int64(0)
+    bb := int64(1)
+    bs := []byte(ns)
+    reverse(bs)
+    for _, c := range bs {
+        total += int64(strings.IndexByte(digits, c)) * bb
+        bb *= b
+    }
+    return total, nil
+}
+
+func main() {
+    numbers := []int64{10, 146, 15, -942, 1488588316238}
+    bases := []int64{-2, -3, -10, -62, -62}
+    for i := 0; i < len(numbers); i++ {
+        n := numbers[i]
+        b := bases[i]
+        ns, err := encodeNegBase(n, b)
+        if err != nil {
+            log.Fatal(err)
+        }
+        fmt.Printf("%13d encoded in base %-3d = %s\n", n, b, ns)
+        n, err = decodeNegBase(ns, b)
+        if err != nil {
+            log.Fatal(err)
+        }
+        fmt.Printf("%13s decoded in base %-3d = %d\n\n", ns, b, n)
+    }
+}