Iterate digit by given integer

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Do you ever meet the question to sum all digits from the input, for example given 112 so the sum of the number is 4.

Naïve approach is to convert to string, then read character one by one. Typecast to integer, then sum all data. The simple ways to typecast rune to int using int(r - ‘0’).

func Solution1(n int) int {
	sum := 0
	for _, r := range fmt.Sprintf(“%d”, n) {
		sum += int(r -0’)
	return sum

Another way is to use an arithmetic approach by utilizing mod and division. Here are the example codes:

func Solution2(n int) int {
	sum := 0
	for n > 0 {
		digit := n % 10
		sum += digit
		n /= 10
	return sum

So which one to use? Let’s see the benchmark result first.

go test -bench=Sum -benchmem -shuffle=on
-test.shuffle 1673764987422236824
goos: linux
goarch: amd64
cpu: AMD Ryzen 7 5800H with Radeon Graphics
BenchmarkSolution2-4    241413471                5.342 ns/op           0 B/op          0 allocs/op
BenchmarkSolution1-4    14215688                84.96 ns/op           16 B/op          1 allocs/op
ok     3.091s

The result of the benchmark Solution2 outclass Solution1 and even 0 allocation. If you encounter the similar problem to do any logic with digit from given integer, you can use the Solution2 approach to avoid time limit platform.

cp go practice