go - 在golang中使用for循环来反转字符串效率低吗？

Question

我是这样做的 Golang ：

func reverseStr(str string) string {
    var reversed string

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

    return reversed
}

我是初学者，现在不能做得更好，但我仍在学习。我想知道我的方法是否比我在网上看到的使用符文的方法效率低：

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)
}

标签： go

Answer 1

我想知道我的方法是否比我在网上看到的使用符文的方法效率低

与符文或for循环无关。您的方法一遍又一遍地构建和重建并重建字符串。而另一个通过简单地交换字符来就地反转字符串。更大的字符串只会变得更糟。

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.")
    }
}

结果

$ 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