16: power digit sum

16_power_digit_sum/main.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"fmt"
+	"math/big"
+	"strconv"
+)
+
+func main() {
+	n := &big.Int{}
+	n.SetInt64(1024)
+	p := (&big.Int{}).SetInt64(1)
+	for i := 0; i < 100; i++ {
+		p = p.Mul(p, n)
+	}
+	sum, err := SumDigits(p.String())
+	if err != nil {
+		panic(err)
+	}
+	fmt.Println("product:", p.String(), "sum:", sum)
+}
+
+func SumDigits(input string) (int, error) {
+	l := len(input)
+	sum := 0
+	for i := 0; i < l; i++ {
+		n, err := strconv.Atoi(input[i : i+1])
+		if err != nil {
+			return 0, fmt.Errorf("invalid input: %s", input)
+		}
+		sum += n
+	}
+	return sum, nil
+}