一、介绍pprof

go test -bench . -cpuprofile cpu.out

go tool pprof cpu.out

指定某个测试_test.go文件

go test -bench . -v nonrepeating_end_test.go

go test -bench . -cpuprofile cpu.out -v nonrepeating_end_test.go

测试更多方面的信息

go test -bench . -cpuprofile cpu.out

查看CPU结果

go tool pprof cpu.out //此时进入交互式命令，可以输入help查看帮助web //自动弹出网页展示svg图查看结果

注意，如果报错：Failed to execute dot. Is Graphviz installed? Error: exec: "dot": executable file not found in %PATH%

请到/download/下载Graphviz, 并配置到环境变量中,将bin目录配置到PATH。

二、实践

1.第一个版本代码

package mainimport ("testing")func lengthOfNonRepeatingSubStr(s string) int {//lastOccurred := make(map[byte]int)lastOccurred := make(map[rune]int)start := 0maxLength := 0//for i, ch := range []byte(s) {for i, ch := range []rune(s) {if lastI, ok := lastOccurred[ch]; ok && lastI >= start {start = lastOccurred[ch] + 1}if i-start+1 > maxLength {maxLength = i - start + 1}lastOccurred[ch] = i}return maxLength}func TestSubstr(t *testing.T) {tests := []struct {s stringans int} {// Normal cases{"abcabcbb", 3},{"pwwkew", 3},// Edge cases{"", 0},{"b", 1},{"bbbbbbbb", 1},{"abcabcabcd", 4},// Chinense cases{"这里是慕课网", 6},{"一二三二一", 3},{"黑化肥挥发发灰会花飞灰化肥挥发发黑会飞花", 8},}for _, tt := range tests {actual := lengthOfNonRepeatingSubStr(tt.s)if actual != tt.ans {t.Errorf("got %d for input %s; " +"expected %d",actual, tt.s, tt.ans)}}}func BenchmarkSubstr(b *testing.B) {s := "黑化肥挥发发灰会花飞灰化肥挥发发黑会飞花"ans := 8for i := 0; i < b.N; i++ {actual := lengthOfNonRepeatingSubStr(s)if actual != ans {b.Errorf("got %d for input %s; " +"expected %d",actual, s, ans)}}}

发现性能差在map赋值，rune的utf8 decode

2.

将map（hash实现）修改slice

package mainimport ("testing")func lengthOfNonRepeatingSubStr(s string) int {//lastOccurred := make(map[byte]int)//lastOccurred := make(map[rune]int)// 测试性能优化// stores las occurred pos + 1.// 0 means not seenvar lastOccurred = make([]int, 0xffff)start := 0maxLength := 0//for i, ch := range []byte(s) {for i, ch := range []rune(s) {if lastI := lastOccurred[ch]; lastI > start {start = lastI}if i-start+1 > maxLength {maxLength = i - start + 1}lastOccurred[ch] = i + 1}return maxLength}func TestSubstr(t *testing.T) {tests := []struct {s stringans int} {// Normal cases{"abcabcbb", 3},{"pwwkew", 3},// Edge cases{"", 0},{"b", 1},{"bbbbbbbb", 1},{"abcabcabcd", 4},// Chinense cases{"这里是慕课网", 6},{"一二三二一", 3},{"黑化肥挥发发灰会花飞灰化肥挥发发黑会飞花", 8},}for _, tt := range tests {actual := lengthOfNonRepeatingSubStr(tt.s)if actual != tt.ans {t.Errorf("got %d for input %s; " +"expected %d",actual, tt.s, tt.ans)}}}func BenchmarkSubstr(b *testing.B) {s := "黑化肥挥发发灰会花飞灰化肥挥发发黑会飞花"ans := 8for i := 0; i < b.N; i++ {actual := lengthOfNonRepeatingSubStr(s)if actual != ans {b.Errorf("got %d for input %s; " +"expected %d",actual, s, ans)}}}

发现图像变得复杂，耗时花在gc上，垃圾回收

3.

package mainimport ("testing")var lastOccurred = make([]int, 0xffff)func lengthOfNonRepeatingSubStr(s string) int {//lastOccurred := make(map[byte]int)//lastOccurred := make(map[rune]int)// 测试性能优化// stores las occurred pos + 1.// 0 means not seenfor i := range lastOccurred {lastOccurred[i] = 0}start := 0maxLength := 0//for i, ch := range []byte(s) {for i, ch := range []rune(s) {if lastI := lastOccurred[ch]; lastI > start {start = lastI}if i-start+1 > maxLength {maxLength = i - start + 1}lastOccurred[ch] = i + 1}return maxLength}func TestSubstr(t *testing.T) {tests := []struct {s stringans int} {// Normal cases{"abcabcbb", 3},{"pwwkew", 3},// Edge cases{"", 0},{"b", 1},{"bbbbbbbb", 1},{"abcabcabcd", 4},// Chinense cases{"这里是慕课网", 6},{"一二三二一", 3},{"黑化肥挥发发灰会花飞灰化肥挥发发黑会飞花", 8},}for _, tt := range tests {actual := lengthOfNonRepeatingSubStr(tt.s)if actual != tt.ans {t.Errorf("got %d for input %s; " +"expected %d",actual, tt.s, tt.ans)}}}func BenchmarkSubstr(b *testing.B) {s := "黑化肥挥发发灰会花飞灰化肥挥发发黑会飞花"ans := 8for i := 0; i < b.N; i++ {actual := lengthOfNonRepeatingSubStr(s)if actual != ans {b.Errorf("got %d for input %s; " +"expected %d",actual, s, ans)}}}

可以发现耗时消耗在

for i := range lastOccurred {

lastOccurred[i] = 0

}

所以我们，准备一个长的字符串，保证最大的耗时不是在memclr

4.

package mainimport ("testing")var lastOccurred = make([]int, 0xffff)func lengthOfNonRepeatingSubStr(s string) int {//lastOccurred := make(map[byte]int)//lastOccurred := make(map[rune]int)// 测试性能优化// stores las occurred pos + 1.// 0 means not seenfor i := range lastOccurred {lastOccurred[i] = 0}start := 0maxLength := 0//for i, ch := range []byte(s) {for i, ch := range []rune(s) {if lastI := lastOccurred[ch]; lastI > start {start = lastI}if i-start+1 > maxLength {maxLength = i - start + 1}lastOccurred[ch] = i + 1}return maxLength}func TestSubstr(t *testing.T) {tests := []struct {s stringans int} {// Normal cases{"abcabcbb", 3},{"pwwkew", 3},// Edge cases{"", 0},{"b", 1},{"bbbbbbbb", 1},{"abcabcabcd", 4},// Chinense cases{"这里是慕课网", 6},{"一二三二一", 3},{"黑化肥挥发发灰会花飞灰化肥挥发发黑会飞花", 8},}for _, tt := range tests {actual := lengthOfNonRepeatingSubStr(tt.s)if actual != tt.ans {t.Errorf("got %d for input %s; " +"expected %d",actual, tt.s, tt.ans)}}}func BenchmarkSubstr(b *testing.B) {s := "黑化肥挥发发灰会花飞灰化肥挥发发黑会飞花"for i := 0; i < 13; i++ {s = s + s}b.Logf("len(s) = %d", len(s))ans := 8// 防止生成s计算在时间里b.ResetTimer()for i := 0; i < b.N; i++ {actual := lengthOfNonRepeatingSubStr(s)if actual != ans {b.Errorf("got %d for input %s; " +"expected %d",actual, s, ans)}}}

因为现在字符串很长，所以decode占用耗时最大

总结：

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