使用闭包实现拓扑排序
,考虑这样一个问题:给定一些计算机课程,每个课程都有前置课程,只有完成了前置课程才可以开始当前课程的学习;我们的目标是选择出一组课程,这组课程必须确保按顺序学习时,能全部被完成。每个课程的前置课程如下:
// prereqs记录了每个课程的前置课程
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"},
}
使用dfs,但是golang的dfs实现有点不一样,如果使用闭包的话。
import (
"fmt"
"sort"
)
func f(p map[string][]string) {
for i,c :=range topoSort(p){
fmt.Printf("%d: %s
", i+1, c)
}
}
//拓扑排序
func topoSort(m map[string][]string) []string {
var order []string
visited := make(map[string]bool)
//其实并没有运行,只是定义声明了visitAll函数而已
var visitAll func(items []string)
visitAll = func(items []string){
for _,item := range items{
if !visited[item] {
visited[item] = true
visitAll(m[item])
//递归入栈
order = append(order,item)
}
}
}
//topo排序真正的流程
var keys []string
for key:=range m{
keys = append(keys,key)
}
//保证输出顺序固定
sort.Strings(keys)
visitAll(keys)
return order
}