exercises of Go tour

EquivalentBinaryTrees.go

package main

import (
	"golang.org/x/tour/tree"
	"fmt"
)

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {
	WalkTree(t, ch)
	close(ch)
}

//中序遍历
func WalkTree(t *tree.Tree, ch chan int) {
	if t.Left != nil {
		WalkTree(t.Left, ch)
	}
	
	ch <- t.Value
	
	if t.Right != nil {
		WalkTree(t.Right, ch)
	}
}

// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
	ch1, ch2 := make(chan int), make(chan int)
	go Walk(t1, ch1)
	go Walk(t2, ch2)
	
	for {
		a1, ok1 := <-ch1
		a2, ok2 := <-ch2
		if a1 != a2 || ok1 != ok2 {
			return false
		}
		if ok1 == false {
			break	
		}
	}
	return true
}

func main() {
	ch := make(chan int)
	go Walk(tree.New(1), ch)
	for v := range ch {
		fmt.Printf("%v ", v)
	}
	fmt.Println()
	fmt.Println(Same(tree.New(1), tree.New(2)))
	fmt.Println(Same(tree.New(1), tree.New(1)))
}

FibonacciClosure.go

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
	i := 0
	return func() int {
		ret := recursive(i)
		i++
		return ret
	}
}

func recursive(n int) int {
	if n <= 1 {
		return n
	} else {
		return recursive(n-1) + recursive(n-2)
	}
}

func nonorecursive(n int) int {
	x, y := 0, 1
	for i := 0; i < n; i++ {
		t := x
		x = y
		y = t + y
	}
	return x
}

func main() {
	f := fibonacci()
	for i := 0; i < 20; i++ {
		fmt.Println(f())
	}
}

rot13Reader.go

package main

import (
	"io"
	"os"
	"strings"
)

var src = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
var des = "NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm"

type rot13Reader struct {
	r io.Reader
}

func (r13 rot13Reader) Read(data []byte) (n int, e error) {
	n, e = r13.r.Read(data)
	
	for i, v := range data {
		if v >= 'A' && v <= 'Z' || v >= 'a' && v <= 'z' {
			data[i] = des[strings.IndexByte(src, v)]
		}
	}
	
	return
}

func main() {
	s := strings.NewReader("Lbh penpxrq gur pbqr!")
	r := rot13Reader{s}
	io.Copy(os.Stdout, &r)
}

WebCrawler.go

package main

import (
	"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)
}

// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher, ch chan string) {
	// TODO: Fetch URLs in parallel.
	// TODO: Don't fetch the same URL twice.
	// This implementation doesn't do either:
	defer close(ch)
	
	if depth <= 0 || !cache.putIfAbsence(url) {
		return
	}
	body, urls, err := fetcher.Fetch(url)
	if err != nil {
		//fmt.Println(err)
		ch <- fmt.Sprintln(err)
		return
	}
	//fmt.Printf("found: %s %q\n", url, body)
	ch <- fmt.Sprintf("found: %s %q\n", url, body)
	
	var rs []chan string
	for _, u := range urls {
		ch2 := make(chan string)
		rs = append(rs, ch2)
		go Crawl(u, depth-1, fetcher, ch2)
	}
	
	for _, ch3 := range rs {
		for v := range ch3 {
			ch <- v
		}
	}
	
	return
}

func main() {
	ch := make(chan string)
	go func() {
		for v := range ch {
			fmt.Print(v)
		}
	}()
	
	Crawl("https://golang.org/", 4, fetcher, ch)

}

type concurrentMap struct {
	data map[string]int
	mux sync.Mutex
}

func (cm *concurrentMap) putIfAbsence(s string) (success bool) {
	cm.mux.Lock()
	
	if _, exist := cm.data[s]; !exist {
		cm.data[s] = 1
		success = true
		
	} else {
		success = false
	}
	
	cm.mux.Unlock()
	return
}

var cache = concurrentMap {data: make(map[string]int)}

// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult

type fakeResult struct {
	body string
	urls []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/",
		},
	},
}