I need a random password generator for a project, I need to make 10 of them. I found this function (random), but when I run it in a loop, it generates the same passwords. I don't know what's the problem.
func main() {
for i := 0; i < 10; i++ {
a := random()
fmt.Println(a)
}
}
func random() string {
rand.Seed(time.Now().UnixNano())
chars := []rune("abcdefghijklmnopqrstuvwxyz" + "0123456789")
length := 10
var b strings.Builder
for i := 0; i < length; i++ {
b.WriteRune(chars[rand.Intn(len(chars))])
}
str := b.String()
return str
}
Adapting your example code and refactoring it a bit:
package main
import (
"fmt"
"math/rand"
"time"
)
func main() {
rp := newRandPass(rand.New(rand.NewSource(time.Now().UnixNano())), 10, 10)
fmt.Println(rp.passwords())
}
type RandPass struct {
r *rand.Rand
num int
len int
}
func newRandPass(r *rand.Rand, num, len int) *RandPass {
return &RandPass{r, num, len}
}
func (r *RandPass) passwords() []string {
chars := []rune("abcdefghijklmnopqrstuvwxyz" + "0123456789")
passwords := make([]string, r.num)
for i := 0; i < r.num; i++ {
s := make([]rune, r.len)
for j := 0; j < r.len; j++ {
s[j] = chars[r.r.Intn(len(chars))]
}
passwords[i] = string(s)
}
return passwords
}
$ go run .
[rt97kzwjwe 5ziim05exh 40dfly93et v5tga5bwv9 avf2p2dpjx hsz4lca0jv 8r7bvvtu5l 9byf3mjq6r sdr2mpo54g cjx4mq6c0t]
Referring to the following benchmarking test codes:
func BenchmarkRuneCountNoDefault(b *testing.B) {
b.StopTimer()
var strings []string
numStrings := 10
for n := 0; n < numStrings; n++{
s := RandStringBytesMaskImprSrc(10)
strings = append(strings, s)
}
jobs := make(chan string)
results := make (chan int)
for i := 0; i < runtime.NumCPU(); i++{
go RuneCountNoDefault(jobs, results)
}
b.StartTimer()
for n := 0; n < b.N; n++ {
go func(){
for n := 0; n < numStrings; n++{
<-results
}
return
}()
for n := 0; n < numStrings; n++{
jobs <- strings[n]
}
}
close(jobs)
}
func RuneCountNoDefault(jobs chan string, results chan int){
for{
select{
case j, ok := <-jobs:
if ok{
results <- utf8.RuneCountInString(j)
} else {
return
}
}
}
}
func BenchmarkRuneCountWithDefault(b *testing.B) {
b.StopTimer()
var strings []string
numStrings := 10
for n := 0; n < numStrings; n++{
s := RandStringBytesMaskImprSrc(10)
strings = append(strings, s)
}
jobs := make(chan string)
results := make (chan int)
for i := 0; i < runtime.NumCPU(); i++{
go RuneCountWithDefault(jobs, results)
}
b.StartTimer()
for n := 0; n < b.N; n++ {
go func(){
for n := 0; n < numStrings; n++{
<-results
}
return
}()
for n := 0; n < numStrings; n++{
jobs <- strings[n]
}
}
close(jobs)
}
func RuneCountWithDefault(jobs chan string, results chan int){
for{
select{
case j, ok := <-jobs:
if ok{
results <- utf8.RuneCountInString(j)
} else {
return
}
default: //DIFFERENCE
}
}
}
//https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-golang
const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
const (
letterIdxBits = 6 // 6 bits to represent a letter index
letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
letterIdxMax = 63 / letterIdxBits // # of letter indices fitting in 63 bits
)
var src = rand.NewSource(time.Now().UnixNano())
func RandStringBytesMaskImprSrc(n int) string {
b := make([]byte, n)
// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
if remain == 0 {
cache, remain = src.Int63(), letterIdxMax
}
if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
b[i] = letterBytes[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return string(b)
}
When I benchmarked both the functions where one function, RuneCountNoDefault has no default clause in the select and the other, RuneCountWithDefault has a default clause, I'm getting the following benchmark:
BenchmarkRuneCountNoDefault-4 200000 8910 ns/op
BenchmarkRuneCountWithDefault-4 5 277798660 ns/op
Checking the cpuprofile generated by the tests, I noticed that the function with the default clause spends a lot of time in the following channel operations:
Why having a default clause in the goroutine's select makes it slower?
I'm using Go version 1.10 for windows/amd64
The Go Programming Language
Specification
Select statements
If one or more of the communications can proceed, a single one that
can proceed is chosen via a uniform pseudo-random selection.
Otherwise, if there is a default case, that case is chosen. If there
is no default case, the "select" statement blocks until at least one
of the communications can proceed.
Modifying your benchmark to count the number of proceed and default cases taken:
$ go test default_test.go -bench=.
goos: linux
goarch: amd64
BenchmarkRuneCountNoDefault-4 300000 4108 ns/op
BenchmarkRuneCountWithDefault-4 10 209890782 ns/op
--- BENCH: BenchmarkRuneCountWithDefault-4
default_test.go:90: proceeds 114
default_test.go:91: defaults 128343308
$
While other cases were unable to proceed, the default case was taken 128343308 times in 209422470, (209890782 - 114*4108), nanoseconds or 1.63 nanoseconds per default case. If you do something small a large number of times, it adds up.
default_test.go:
package main
import (
"math/rand"
"runtime"
"sync/atomic"
"testing"
"time"
"unicode/utf8"
)
func BenchmarkRuneCountNoDefault(b *testing.B) {
b.StopTimer()
var strings []string
numStrings := 10
for n := 0; n < numStrings; n++ {
s := RandStringBytesMaskImprSrc(10)
strings = append(strings, s)
}
jobs := make(chan string)
results := make(chan int)
for i := 0; i < runtime.NumCPU(); i++ {
go RuneCountNoDefault(jobs, results)
}
b.StartTimer()
for n := 0; n < b.N; n++ {
go func() {
for n := 0; n < numStrings; n++ {
<-results
}
return
}()
for n := 0; n < numStrings; n++ {
jobs <- strings[n]
}
}
close(jobs)
}
func RuneCountNoDefault(jobs chan string, results chan int) {
for {
select {
case j, ok := <-jobs:
if ok {
results <- utf8.RuneCountInString(j)
} else {
return
}
}
}
}
var proceeds ,defaults uint64
func BenchmarkRuneCountWithDefault(b *testing.B) {
b.StopTimer()
var strings []string
numStrings := 10
for n := 0; n < numStrings; n++ {
s := RandStringBytesMaskImprSrc(10)
strings = append(strings, s)
}
jobs := make(chan string)
results := make(chan int)
for i := 0; i < runtime.NumCPU(); i++ {
go RuneCountWithDefault(jobs, results)
}
b.StartTimer()
for n := 0; n < b.N; n++ {
go func() {
for n := 0; n < numStrings; n++ {
<-results
}
return
}()
for n := 0; n < numStrings; n++ {
jobs <- strings[n]
}
}
close(jobs)
b.Log("proceeds", atomic.LoadUint64(&proceeds))
b.Log("defaults", atomic.LoadUint64(&defaults))
}
func RuneCountWithDefault(jobs chan string, results chan int) {
for {
select {
case j, ok := <-jobs:
atomic.AddUint64(&proceeds, 1)
if ok {
results <- utf8.RuneCountInString(j)
} else {
return
}
default: //DIFFERENCE
atomic.AddUint64(&defaults, 1)
}
}
}
//https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-golang
const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
const (
letterIdxBits = 6 // 6 bits to represent a letter index
letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
letterIdxMax = 63 / letterIdxBits // # of letter indices fitting in 63 bits
)
var src = rand.NewSource(time.Now().UnixNano())
func RandStringBytesMaskImprSrc(n int) string {
b := make([]byte, n)
// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
if remain == 0 {
cache, remain = src.Int63(), letterIdxMax
}
if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
b[i] = letterBytes[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return string(b)
}
Playground: https://play.golang.org/p/DLnAY0hovQG
I'm trying to scan a matrix from the stdin and simply print it using following code.
package main
import (
"fmt"
)
func print2D(arr [][]int) {
for i:=0; i< len(arr); i++{
for j := 0; j< len(arr[0]); j++{
fmt.Printf("%d ", arr[i][j])
}
fmt.Println()
}
}
func main() {
var arr [6][6]int
for i:= 0 ; i < 6 ;i++ {
for j := 0; j< 6; j++{
fmt.Scanf("%d", &arr[i][j])
}
}
print2D(arr[:])
}
It throws the following error
./main.go:23: cannot use arr[:] (type [][6]int) as type [][]int in
argument to print2D
Is there a way to pass a 2D slice without defining sizes in the function arguments?
Try to write the data directly to the slice and pass it later to the function. Remember array and slices are different types. Moreover, the type [3]int is also different from [4]int (size matters).
package main
import (
"fmt"
)
func print2D(arr [][]int) {
for i := 0; i < len(arr); i++ {
for j := 0; j < len(arr[0]); j++ {
fmt.Printf("%d ", arr[i][j])
}
fmt.Println()
}
}
func main() {
var arr [][]int
for i := 0; i < 6; i++ {
tmp := make([]int, 6)
for j := 0; j < 6; j++ {
fmt.Scanf("%d", &tmp[j])
}
arr = append(arr, tmp)
}
print2D(arr)
}
Is it possible to make multiple line plots with common abscissas axis in gonum/plot?
In matplotlib it would look like this.
Yes, it is possible. You can use plot.Align:
package main
import (
"math/rand"
"os"
"gonum.org/v1/plot"
"gonum.org/v1/plot/plotter"
"gonum.org/v1/plot/vg"
"gonum.org/v1/plot/vg/draw"
"gonum.org/v1/plot/vg/vgimg"
)
func main() {
rand.Seed(int64(0))
const rows, cols = 2, 1
plots := make([][]*plot.Plot, rows)
for j := 0; j < rows; j++ {
plots[j] = make([]*plot.Plot, cols)
for i := 0; i < cols; i++ {
p := randomLinePlot(rand.Intn(10))
// make sure the horizontal scales match
p.X.Min = 0
p.X.Max = 5
plots[j][i] = p
}
}
img := vgimg.New(vg.Points(150), vg.Points(175))
dc := draw.New(img)
t := draw.Tiles{
Rows: rows,
Cols: cols,
}
canvases := plot.Align(plots, t, dc)
for j := 0; j < rows; j++ {
for i := 0; i < cols; i++ {
if plots[j][i] != nil {
plots[j][i].Draw(canvases[j][i])
}
}
}
w, err := os.Create("aligned.png")
if err != nil {
panic(err)
}
png := vgimg.PngCanvas{Canvas: img}
if _, err := png.WriteTo(w); err != nil {
panic(err)
}
}
This generates the following plots in a single PNG file:
You can find another example below the GoDoc entry of plot.Align
I have two strings (they are actually version numbers and they could be any version numbers)
a := "1.05.00.0156"
b := "1.0.221.9289"
I want to compare which one is bigger. How to do it in golang?
There is a nice solution from Hashicorp - https://github.com/hashicorp/go-version
import github.com/hashicorp/go-version
v1, err := version.NewVersion("1.2")
v2, err := version.NewVersion("1.5+metadata")
// Comparison example. There is also GreaterThan, Equal, and just
// a simple Compare that returns an int allowing easy >=, <=, etc.
if v1.LessThan(v2) {
fmt.Printf("%s is less than %s", v1, v2)
}
Some time ago I created a version comparison library: https://github.com/mcuadros/go-version
version.CompareSimple("1.05.00.0156", "1.0.221.9289")
//Returns: 1
Enjoy it!
Here's a general solution.
package main
import "fmt"
func VersionOrdinal(version string) string {
// ISO/IEC 14651:2011
const maxByte = 1<<8 - 1
vo := make([]byte, 0, len(version)+8)
j := -1
for i := 0; i < len(version); i++ {
b := version[i]
if '0' > b || b > '9' {
vo = append(vo, b)
j = -1
continue
}
if j == -1 {
vo = append(vo, 0x00)
j = len(vo) - 1
}
if vo[j] == 1 && vo[j+1] == '0' {
vo[j+1] = b
continue
}
if vo[j]+1 > maxByte {
panic("VersionOrdinal: invalid version")
}
vo = append(vo, b)
vo[j]++
}
return string(vo)
}
func main() {
versions := []struct{ a, b string }{
{"1.05.00.0156", "1.0.221.9289"},
// Go versions
{"1", "1.0.1"},
{"1.0.1", "1.0.2"},
{"1.0.2", "1.0.3"},
{"1.0.3", "1.1"},
{"1.1", "1.1.1"},
{"1.1.1", "1.1.2"},
{"1.1.2", "1.2"},
}
for _, version := range versions {
a, b := VersionOrdinal(version.a), VersionOrdinal(version.b)
switch {
case a > b:
fmt.Println(version.a, ">", version.b)
case a < b:
fmt.Println(version.a, "<", version.b)
case a == b:
fmt.Println(version.a, "=", version.b)
}
}
}
Output:
1.05.00.0156 > 1.0.221.9289
1 < 1.0.1
1.0.1 < 1.0.2
1.0.2 < 1.0.3
1.0.3 < 1.1
1.1 < 1.1.1
1.1.1 < 1.1.2
1.1.2 < 1.2
go-semver is a semantic versioning library for Go. It lets you parse and compare two semantic version strings.
Example:
vA := semver.New("1.2.3")
vB := semver.New("3.2.1")
fmt.Printf("%s < %s == %t\n", vA, vB, vA.LessThan(*vB))
Output:
1.2.3 < 3.2.1 == true
Here are some of the libraries for version comparison:
https://github.com/blang/semver
https://github.com/Masterminds/semver
https://github.com/hashicorp/go-version
https://github.com/mcuadros/go-version
I have used blang/semver.
Eg: https://play.golang.org/p/1zZvEjLSOAr
import github.com/blang/semver/v4
v1, err := semver.Make("1.0.0-beta")
v2, err := semver.Make("2.0.0-beta")
// Options availabe
v1.Compare(v2) // Compare
v1.LT(v2) // LessThan
v1.GT(v2) // GreaterThan
This depends on what you mean by bigger.
A naive approach would be:
package main
import "fmt"
import "strings"
func main() {
a := strings.Split("1.05.00.0156", ".")
b := strings.Split("1.0.221.9289", ".")
for i, s := range a {
var ai, bi int
fmt.Sscanf(s, "%d", &ai)
fmt.Sscanf(b[i], "%d", &bi)
if ai > bi {
fmt.Printf("%v is bigger than %v\n", a, b)
break
}
if bi > ai {
fmt.Printf("%v is bigger than %v\n", b, a)
break
}
}
}
http://play.golang.org/p/j0MtFcn44Z
Based on Jeremy Wall's answer:
func compareVer(a, b string) (ret int) {
as := strings.Split(a, ".")
bs := strings.Split(b, ".")
loopMax := len(bs)
if len(as) > len(bs) {
loopMax = len(as)
}
for i := 0; i < loopMax; i++ {
var x, y string
if len(as) > i {
x = as[i]
}
if len(bs) > i {
y = bs[i]
}
xi,_ := strconv.Atoi(x)
yi,_ := strconv.Atoi(y)
if xi > yi {
ret = -1
} else if xi < yi {
ret = 1
}
if ret != 0 {
break
}
}
return
}
http://play.golang.org/p/AetJqvFc3B
Striving for clarity and simplicity:
func intVer(v string) (int64, error) {
sections := strings.Split(v, ".")
intVerSection := func(v string, n int) string {
if n < len(sections) {
return fmt.Sprintf("%04s", sections[n])
} else {
return "0000"
}
}
s := ""
for i := 0; i < 4; i++ {
s += intVerSection(v, i)
}
return strconv.ParseInt(s, 10, 64)
}
func main() {
a := "3.045.98.0832"
b := "087.2345"
va, _ := intVer(a)
vb, _ := intVer(b)
fmt.Println(va<vb)
}
Comparing versions implies parsing so I believe these 2 steps should be separate to make it robust.
tested in leetcode: https://leetcode.com/problems/compare-version-numbers/
func compareVersion(version1 string, version2 string) int {
len1, len2, i, j := len(version1), len(version2), 0, 0
for i < len1 || j < len2 {
n1 := 0
for i < len1 && '0' <= version1[i] && version1[i] <= '9' {
n1 = n1 * 10 + int(version1[i] - '0')
i++
}
n2 := 0
for j < len2 && '0' <= version2[j] && version2[j] <= '9' {
n2 = n2 * 10 + int(version2[j] - '0')
j++
}
if n1 > n2 {
return 1
}
if n1 < n2 {
return -1
}
i, j = i+1, j+1
}
return 0
}
import (
"fmt"
"strconv"
"strings"
)
func main() {
j := ll("1.05.00.0156" ,"1.0.221.9289")
fmt.Println(j)
}
func ll(a,b string) int {
var length ,r,l int = 0,0,0
v1 := strings.Split(a,".")
v2 := strings.Split(b,".")
len1, len2 := len(v1), len(v2)
length = len2
if len1 > len2 {
length = len1
}
for i:= 0;i<length;i++ {
if i < len1 && i < len2 {
if v1[i] == v2[i] {
continue
}
}
r = 0
if i < len1 {
if number, err := strconv.Atoi(v1[i]); err == nil {
r = number
}
}
l = 0
if i < len2 {
if number, err := strconv.Atoi(v2[i]); err == nil {
l = number
}
}
if r < l {
return -1
}else if r> l {
return 1
}
}
return 0
}
If you can guarantee version strings have same format (i.e. SemVer), you can convert to int and compare int. Here is an implementation for sorting slices of SemVer:
versions := []string{"1.0.10", "1.0.6", "1.0.9"}
sort.Slice(versions[:], func(i, j int) bool {
as := strings.Split(versions[i], ".")
bs := strings.Split(versions[j], ".")
if len(as) != len(bs) || len(as) != 3 {
return versions[i] < versions[j]
}
ais := make([]int, len(as))
bis := make([]int, len(bs))
for i := range as {
ais[i], _ = strconv.Atoi(as[i])
bis[i], _ = strconv.Atoi(bs[i])
}
//X.Y.Z
// If X and Y are the same, compare Z
if ais[0] == bis[0] && ais[1] == bis[1] {
return ais[2] < bis[2]
}
// If X is same, compare Y
if ais[0] == bis[0] {
return ais[1] < bis[1]
}
// Compare X
return ais[0] < bis[0]
})
fmt.Println(versions)
tested in go playground
// If v1 > v2 return '>'
// If v1 < v2 return '<'
// Otherwise return '='
func CompareVersion(v1, v2 string) byte {
v1Slice := strings.Split(v1, ".")
v2Slice := strings.Split(v2, ".")
var maxSize int
{ // Make them both the same size.
if len(v1Slice) < len(v2Slice) {
maxSize = len(v2Slice)
} else {
maxSize = len(v1Slice)
}
}
v1NSlice := make([]int, maxSize)
v2NSlice := make([]int, maxSize)
{
// Convert string to the int.
for i := range v1Slice {
v1NSlice[i], _ = strconv.Atoi(v1Slice[i])
}
for i := range v2Slice {
v2NSlice[i], _ = strconv.Atoi(v2Slice[i])
}
}
var result byte
var v2Elem int
for i, v1Elem := range v1NSlice {
if result != '=' && result != 0 { // The previous comparison has got the answer already.
return result
}
v2Elem = v2NSlice[i]
if v1Elem > v2Elem {
result = '>'
} else if v1Elem < v2Elem {
result = '<'
} else {
result = '='
}
}
return result
}
Convert "1.05.00.0156" to "0001"+"0005"+"0000"+"0156", then to int64.
Convert "1.0.221.9289" to "0001"+"0000"+"0221"+"9289", then to int64.
Compare the two int64 values.
Try it on the Go playground