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