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package main
import (
"crypto/rand"
"fmt"
"math/big"
"os"
"strconv"
"strings"
)
func main() {
if len(os.Args) != 2 {
fmt.Printf("usage: %s <die[+die...]>\n", os.Args[0])
os.Exit(1)
}
dice := strings.Split(os.Args[1], "+")
var sum int64
for _, die := range dice {
if result, err := resolve(die); err != nil {
fmt.Printf("%v\n", err)
os.Exit(1)
} else {
sum += result
}
}
fmt.Printf("%d\n", sum)
}
func resolve(die string) (int64, error) {
// try parsing as a die e.g. 2d6
var (
num int
sides int64
)
if fields, err := fmt.Sscanf(die, "%dd%d", &num, &sides); err == nil && fields == 2 {
var sum int64
for i := 0; i < num; i++ {
if r, err := roll(sides); err != nil {
return 0, err
} else {
sum += r
}
}
return sum, nil
}
// try just parsing as a number, e.g. +5
if x, err := strconv.Atoi(die); err != nil {
return 0, fmt.Errorf("unrecognized die: %s", die)
} else {
return int64(x), nil
}
}
func roll(sides int64) (int64, error) {
r, err := rand.Int(rand.Reader, big.NewInt(sides))
if err != nil {
return 0, err
}
return 1 + r.Int64(), nil
}
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