通过在golang中使用for循环来反转字符串效率低下？

Question

I did it like this Golang:

func reverseStr(str string) string {
    var reversed string

    for i := len(str) - 1; i >= 0; i-- {
        reversed += string(str[i])
    }

    return reversed
}

I'm a beginner and can't do better for now, but I'm still learning. I'd like to know is my method less efficient than the ones I saw online that use runes:

func reverse(s string) string {
    chars := []rune(s)
    for i, j := 0, len(chars)-1; i < j; i, j = i+1, j-1 {
        chars[i], chars[j] = chars[j], chars[i]
    }
    return string(chars)
}

Answer 1

I'd like to know is my method less efficient than the ones I saw online that use runes

Nothing to do with runes or for loop. Your method builds and rebuilds and rebuilds a string, over and over. Whereas the other one reverses the string in-place, by simply swapping characters. And the difference is only getting worse with larger strings.

package main

import "testing"

func reverseConcat(str string) string {
    var reversed string

    for i := len(str) - 1; i >= 0; i-- {
        reversed += string(str[i])
    }

    return reversed
}

func reverseSwapRunes(s string) string {
    chars := []rune(s)
    for i, j := 0, len(chars)-1; i < j; i, j = i+1, j-1 {
        chars[i], chars[j] = chars[j], chars[i]
    }
    return string(chars)
}

func BenchmarkConcatSmall(b *testing.B) {
    for i := 0; i < b.N; i++ {
        reverseConcat("hello world")
    }
}

func BenchmarkSwapRunesSmall(b *testing.B) {
    for i := 0; i < b.N; i++ {
        reverseSwapRunes("hello world")
    }
}

func BenchmarkConcatLarger(b *testing.B) {
    for i := 0; i < b.N; i++ {
        reverseConcat("Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.")
    }
}

func BenchmarkSwapRunesLarger(b *testing.B) {
    for i := 0; i < b.N; i++ {
        reverseSwapRunes("Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.")
    }
}

Results

$ go test -bench . -benchmem
goos: linux
goarch: amd64
BenchmarkConcatSmall-8           5000000           329 ns/op          80 B/op         10 allocs/op
BenchmarkSwapRunesSmall-8       20000000           117 ns/op          16 B/op          1 allocs/op
BenchmarkConcatLarger-8            30000         44877 ns/op      172833 B/op        573 allocs/op
BenchmarkSwapRunesLarger-8        300000          5353 ns/op        2944 B/op          2 allocs/op