[日常] Go语言圣经-匿名函数习题

package main

import (
        "fmt"
        "golang.org/x/net/html"
        "net/http"
        "sort"
)

var prereqs = map[string][]string{
        "algorithms": {"data structures"},
        "calculus":   {"linear algebra"},
        "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() {
        for i, course := range topoSort(prereqs) {
                fmt.Printf("%d:\t%s\n", i+1, course)
        }   
        fmt.Println("------------------------")
        for k, v := range topoSort2(prereqs) {
                fmt.Printf("%d:\t%s\n", k, v)
        }   
        fmt.Println("------------------------")
        outline("http://mail.sina.net")
}

/*
练习5.10： 重写topoSort函数，用map代替切片并移除对key的排序代码。验证结果的正确性（结果不唯一）。
*/
func topoSort2(m map[string][]string) map[int]string {
        var order = make(map[int]string)
        index := 1
        seen := make(map[string]bool)
        var visitAll func(items []string)
        visitAll = func(items []string) {
                for _, item := range items {
                        if !seen[item] {
                                seen[item] = true
                                visitAll(m[item])
                                order[index] = item
                                index++
                        }
                }
        }
        var keys []string
        for key := range m {
                keys = append(keys, key)
        }
        visitAll(keys)
        return order
}
func topoSort(m map[string][]string) []string {
        var order []string
        seen := make(map[string]bool)
        var visitAll func(items []string)
        visitAll = func(items []string) {
                for _, item := range items {
                        if !seen[item] {
                                seen[item] = true
                                visitAll(m[item])
                                order = append(order, item)
                        }
                }
        }
        var keys []string
        for key := range m {
                keys = append(keys, key)
        }
        sort.Strings(keys)
        visitAll(keys)
        return order
}

/*
练习5.11： 现在线性代数的老师把微积分设为了前置课程。完善topSort，使其能检测有向图中的环。
等着去看数据结构再看这个题
*/

/*
练习5.12： gopl.io/ch5/outline2（5.5节）的startElement和endElement共用了全局变量depth，将它们修改为匿名函数，使其共享outline中的局部变量。
*/
func outline(url string) (string, error) {
        resp, err := http.Get(url)
        if err != nil {
                return "", err
        }
        doc, _ := html.Parse(resp.Body)
        //使用匿名函数实现
        var depth int
        var startElement func(n *html.Node)
        var endElement func(n *html.Node)

        startElement = func(n *html.Node) {
                if n.Type == html.ElementNode {
                        attr := ""
                        for _, a := range n.Attr {
                                attr += " " + a.Key + "=" + "\"" + a.Val + "\" "
                        }
                        fmt.Printf("%*s<%s%s", depth*2, "", n.Data, attr)
                        depth++
                }
                if n.Type == html.ElementNode && n.FirstChild == nil && n.Data != "script" {
                        fmt.Printf("/>\n")
                } else if n.Type == html.ElementNode {
                        fmt.Printf(">\n")
                }

                if n.Type == html.TextNode {
                        fmt.Printf("%*s %s\n", depth*2, "", n.Data)
                }
        }
        endElement = func(n *html.Node) {
                if n.Type == html.ElementNode && n.FirstChild == nil && n.Data != "script" {
                        depth--
                        fmt.Printf("\n")
                        return
                }
                if n.Type == html.ElementNode {
                        depth--

                        fmt.Printf("%*s</%s>\n", depth*2, "", n.Data)
                }
        }
        //1.使用函数值
        forEachNode(doc, startElement, endElement)
        resp.Body.Close()
        return "", nil
}

func forEachNode(n *html.Node, pre, post func(n *html.Node)) {
        //显式的调用一下
        if pre != nil {
                pre(n)
        }

        //fmt.Println(n.Data)
        for c := n.FirstChild; c != nil; c = c.NextSibling {
                forEachNode(c, pre, post)
        }
        if post != nil {
                post(n)
        }
}