《go语言圣经》习题答案-第5章

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5.11

package mainimport ("fmt""sort"
)var dict = map[string][]string{"algorithms":     {"data structures"},"calculus":       {"linear algebra"},"linear algebra": {"calculus"},"compilers": {"data structures","formal languages","computer organization",},"data structures":       {"discrete math"},"databases":             {"data structures"},"discrete math":         {"intro to programming"},"formal languages":      {"discrete math"},"networks":              {"operating systems"},"operating systems":     {"data structures", "computer organization"},"programming languages": {"data structures", "computer organization"},
}func main() {list, ok := toposort(dict)if !ok {fmt.Println("存在环")return}for i, s := range list {fmt.Printf("%d\t%s\n", i+1, s)}
}func toposort(dict map[string][]string) ([]string, bool) {var list []stringseen := make(map[string]bool)wait := make(map[string]bool)var visitAll func(items []string) boolvisitAll = func(items []string) bool {for _, item := range items {if !seen[item] {seen[item] = truewait[item] = trueif !visitAll(dict[item]) {return false}list = append(list, item)wait[item] = false} else if wait[item] {return false}}return true}var keys []stringfor key := range dict {keys = append(keys, key)}sort.Strings(keys)if !visitAll(keys) {return nil, false}return list, true
}

5.13

package mainimport ("fmt""io/ioutil""net/http""strings"neturl "net/url""os""golang.org/x/net/html""gopl.io/util"
)func Extract(url string, hosts map[string]bool) ([]string, error) {resp, err := http.Get(url)if err != nil {return nil, err}if resp.StatusCode != http.StatusOK {resp.Body.Close()return nil, fmt.Errorf("getting %s: %s", url, resp.Status)}content, _ := ioutil.ReadAll(resp.Body)contentstr := string(content)doc, err := html.Parse(strings.NewReader(contentstr))resp.Body.Close()if err != nil {return nil, fmt.Errorf("parsing %s as HTML: %v", url, err)}var links []stringvisitNode := func(n *html.Node) {u, err := neturl.Parse(url)if err != nil {fmt.Printf("解析路径%s失败 %s\n", url, err)}dir := u.Hostif n.Type == html.ElementNode && n.Data == "title" && hosts[dir] {name := n.FirstChild.DatamkErr := os.Mkdir(dir, os.ModePerm)if mkErr != nil && os.IsNotExist(mkErr) {fmt.Printf("创建文件夹[%s]失败 %s\n", dir, mkErr)}fn := dir + "/" + name + ".html"file, err := os.OpenFile(fn, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)if err != nil {fmt.Printf("创建文件[%s]失败 %s\n", fn, err)} else {fmt.Printf("保存文件 %s\n", fn)file.WriteString(contentstr)file.Close()}}if n.Type == html.ElementNode && n.Data == "a" {for _, a := range n.Attr {if a.Key != "href" {continue}link, err := resp.Request.URL.Parse(a.Val)if err != nil {continue}links = append(links, link.String())}}}util.ForEachNode(doc, visitNode, nil)return links, nil
}

package mainimport ("fmt""log""net/url""os""strings"
)func main() {urls := os.Args[1:]seen := map[string]bool{}toVisit := []string{}toVisit = append(toVisit, urls...)hosts := map[string]bool{}for _, u := range urls {uu, err := url.Parse(u)if err == nil {hosts[uu.Host] = true}}for len(toVisit) != 0 {links := toVisittoVisit = nilfor _, link := range links {if strings.HasSuffix(link, "/") {link = link[:len(link)-1]}if !seen[link] {fmt.Println(link)seen[link] = truel, err := Extract(link, hosts)if err != nil {log.Print(err)}toVisit = append(toVisit, l...)}}}
}

5.14

package mainimport ("fmt""io/ioutil""os"
)func Bfs(f func(item string) []string, worklist []string) {seen := make(map[string]bool)for len(worklist) > 0 {items := worklistworklist = nilfor _, item := range items {if !seen[item] {seen[item] = trueworklist = append(worklist, f(item)...)}}}
}func crawlCourse() {var dict = map[string][]string{"algorithms":     {"data structures"},"calculus":       {"linear algebra"},"linear algebra": {"calculus"},"compilers": {"data structures","formal languages","computer organization",},"data structures":       {"discrete math"},"databases":             {"data structures"},"discrete math":         {"intro to programming"},"formal languages":      {"discrete math"},"networks":              {"operating systems"},"operating systems":     {"data structures", "computer organization"},"programming languages": {"data structures", "computer organization"},}f := func(s string) []string {fmt.Println(s)return dict[s]}items := []string{}for k, _ := range dict {items = append(items, k)}Bfs(f, items)
}func crawlFile() {root := []string{"gopl.io"}f := func(path string) []string {s, _ := os.Stat(path)if !s.IsDir() {fmt.Println(path)return nil}rd, err := ioutil.ReadDir(path)if err != nil {fmt.Printf("read dir[%s] faild %s\n", path, err)return nil}files := []string{}for _, fi := range rd {files = append(files, path+"/"+fi.Name())}return files}Bfs(f, root)
}func main() {crawlCourse()crawlFile()
}

5.15

package mainimport ("fmt""math"
)func main() {fmt.Println(max())fmt.Println(max(4))fmt.Println(max(8, 4, 9))
}func max(vals ...int) int {if len(vals) == 0 {return math.MaxInt}m := math.MinIntfor _, n := range vals {if n > m {m = n}}return m
}

package mainimport ("fmt"
)func main() {fmt.Println(max(4))fmt.Println(max(8, 4, 9))
}func max(val int, vals ...int) int {for _, n := range vals {if n > val {val = n}}return val
}

5.16

package mainimport ("bytes""fmt"
)func main() {fmt.Println(join(",", []string{"wewei"}...))fmt.Println(join(",", []string{}...))fmt.Println(join("", []string{"weiwei", "zheng"}...))
}func join(sep string, strs ...string) string {var buf bytes.Buffers := ""for _, str := range strs {buf.WriteString(s)buf.WriteString(str)s = sep}return buf.String()
}

5.17

package mainimport ("fmt""net/http""os""golang.org/x/net/html"
)func main() {resp, err := http.Get("https://www.hao123.com")if err != nil {fmt.Fprintf(os.Stderr, "echo: %v\n", err)os.Exit(1)}defer resp.Body.Close()doc, err := html.Parse(resp.Body)if err != nil {fmt.Fprintf(os.Stderr, "echo: %v\n", err)os.Exit(1)}nodes1 := ElementsByTagName(doc, "div")nodes2 := ElementsByTagName(doc, "a")nodes3 := ElementsByTagName(doc, "div", "a")fmt.Printf("%d, %d, %d\n", len(nodes1), len(nodes2), len(nodes3))
}func ElementsByTagName(doc *html.Node, names ...string) []*html.Node {tags := make(map[string]bool)for _, n := range names {tags[n] = true}var list []*html.Nodevar forEachNode func(doc *html.Node)forEachNode = func(doc *html.Node) {if doc.Type == html.ElementNode && tags[doc.Data] {list = append(list, doc)}for c := doc.FirstChild; c != nil; c = c.NextSibling {forEachNode(c)}}forEachNode(doc)return list}

5.19

package mainimport ("fmt"
)func main() {fmt.Println(f())
}func f() (code int) {defer func() {if p := recover(); p != nil {code = 1}}()panic("")
}

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《go语言圣经》习题答案-第5章

5.11

5.13

5.14

5.15

5.16

5.17

5.19

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