Go基础知识学习-习题题解

这里给出来官方教程中部分题目的答案，都是自己练习的时候写的，可以参考来提供思路。

当然了，练习还是最好自己写，要不对相关的知识点不可能理解透彻。

Exercise: Loops and Functions

package mainimport ("fmt"
)func Sqrt(x float64) float64 {z:=1.0for i:=0;i<10;i++{z -= (z*z - x) / (2*z)fmt.Println(z)}return z
}func main() {fmt.Println(Sqrt(2))
}

Exercise: Slices

package mainimport ("golang.org/x/tour/pic"
)func Pic(dx, dy int) [][]uint8 {pic := make([][]uint8, dx)for x := range pic {pic[x] = make([]uint8, dy)for y := range pic[x] {pic[x][y] = uint8(255)}}return pic
}func main() {pic.Show(Pic)
}

Exercise: Maps

package mainimport ("golang.org/x/tour/wc""strings"
)func WordCount(s string) map[string]int {dataMap:=make(map[string]int)strArr:=strings.Fields(s)for _,x:= range strArr{dataMap[x]+=1}return dataMap
}func main() {wc.Test(WordCount)
}

Exercise: Fibonacci closure

package mainimport "fmt"// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {le:=-1ri:=1return func()int{fib:=le+rile=riri=fibreturn fib}
}func main() {f := fibonacci()for i := 0; i < 10; i++ {fmt.Println(f())}
}

Exercise: Stringers

package mainimport "fmt"type IPAddr [4]byte// TODO: Add a "String() string" method to IPAddr.func (ip IPAddr) String() string{return fmt.Sprintf("%d.%d.%d.%d", ip[0], ip[1], ip[2], ip[3])
}func int2str(a byte) string{return string(int(a+'0'))
}func main() {hosts := map[string]IPAddr{"loopback":  {127, 0, 0, 1},"googleDNS": {8, 8, 8, 8},}for name, ip := range hosts {fmt.Printf("%v: %v\n", name, ip)}
}

Exercise: Errors

package mainimport ("fmt"
)type ErrNegativeSqrt float64func (e ErrNegativeSqrt) Error() string{return fmt.Sprintf("cannot Sqrt negative number: %v",float64(e))
}func Sqrt(x float64) (float64, error) {if x < 0{return 0,ErrNegativeSqrt(x)}z := 1.0for i := 0; i < 10; i++ {z -= (z*z - x) / (2 * z)}return z, nil
}func main() {fmt.Println(Sqrt(2))fmt.Println(Sqrt(-2))
}

Exercise: Readers

 package mainimport "golang.org/x/tour/reader"type MyReader struct{}// TODO: Add a Read([]byte) (int, error) method to MyReader.func (MyReader) Read(buf []byte)(int,error){buf[0]='A'return 1,nil
}func main() {reader.Validate(MyReader{})
}

Exercise: rot13Reader

import ("io""os""strings"
)type rot13Reader struct {r io.Reader
}func (rot13 *rot13Reader) Read(buf []byte) (int, error) {count, err := rot13.r.Read(buf)if count > 0 && err == nil {for i, c := range buf {if c >= 'a' && c <= 'z'{buf[i] = 'a'+(c-'a' + 13) % 26}else if c >= 'A' && c <= 'Z'{buf[i] = 'A'+(c-'A' + 13) % 26}}}return count, err
}func main() {s := strings.NewReader("Lbh penpxrq gur pbqr!")r := rot13Reader{s}io.Copy(os.Stdout, &r)
}

Exercise: Images

package mainimport ("golang.org/x/tour/pic""image/color""image"
)type Image struct{}func (Image) Bounds() image.Rectangle{return image.Rect(0,0,233,233)
}func (Image) ColorModel() color.Model{return color.RGBAModel;
}func (Image) At(x,y int) color.Color{return color.RGBA{uint8(x),uint8(x+y),uint8(x-y),uint8(y)}
}func main() {m := Image{}pic.ShowImage(m)
}

Exercise: Equivalent Binary Trees

package mainimport ("fmt""golang.org/x/tour/tree"
)/*type Tree struct {Left  *TreeValue intRight *Tree
}
*/// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {if t != nil {Walk(t.Left, ch)ch <- t.ValueWalk(t.Right, ch)}
}// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {ch1 :=make(chan int,10)ch2:=make(chan int,10)go Walk(t1,ch1)go Walk(t2,ch2)for i:=0;i<10;i++{if <-ch1 != <- ch2{return false}}return true
}func main() {ch:=make(chan int,10)go Walk(tree.New(1), ch)for i := 0; i < 10; i++ { // Read and print 10 values from the channelfmt.Println(<-ch)}fmt.Println(Same(tree.New(1), tree.New(1))) // should print truefmt.Println(Same(tree.New(1), tree.New(2))) // should print false
}

Exercise: Web Crawler

package mainimport ("fmt""sync"
)type Fetcher interface {// Fetch returns the body of URL and// a slice of URLs found on that page.Fetch(url string) (body string, urls []string, err error)
}type urlCache struct{mux sync.Mutexurls map[string]bool
}
func (cache *urlCache) add(url string){cache.mux.Lock()cache.urls[url] = truecache.mux.Unlock()
}func (cache *urlCache) isVisited(url string) bool{cache.mux.Lock()defer cache.mux.Unlock()return cache.urls[url]
}var visited = urlCache{urls: make(map[string]bool)}// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher,wg *sync.WaitGroup) {defer wg.Done()// TODO: Fetch URLs in parallel.// TODO: Don't fetch the same URL twice.// This implementation doesn't do either:if depth <= 0||visited.isVisited(url) {return}visited.add(url)body, urls, err := fetcher.Fetch(url)if err != nil {fmt.Println(err)return}fmt.Printf("found: %s %q\n", url, body)for _, u := range urls {wg.Add(1)go Crawl(u, depth-1, fetcher,wg)}return
}func main() {var wg sync.WaitGroupwg.Add(1)go Crawl("https://golang.org/", 4, fetcher,&wg)wg.Wait()
}// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResulttype fakeResult struct {body stringurls []string
}func (f fakeFetcher) Fetch(url string) (string, []string, error) {if res, ok := f[url]; ok {return res.body, res.urls, nil}return "", nil, fmt.Errorf("not found: %s", url)
}// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{"https://golang.org/": &fakeResult{"The Go Programming Language",[]string{"https://golang.org/pkg/","https://golang.org/cmd/",},},"https://golang.org/pkg/": &fakeResult{"Packages",[]string{"https://golang.org/","https://golang.org/cmd/","https://golang.org/pkg/fmt/","https://golang.org/pkg/os/",},},"https://golang.org/pkg/fmt/": &fakeResult{"Package fmt",[]string{"https://golang.org/","https://golang.org/pkg/",},},"https://golang.org/pkg/os/": &fakeResult{"Package os",[]string{"https://golang.org/","https://golang.org/pkg/",},},
}