gopl-zh.github.com/vendor/gopl.io/ch5/toposort/main.go

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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// See page 136.
// The toposort program prints the nodes of a DAG in topological order.
package main
import (
"fmt"
"sort"
)
//!+table
// prereqs maps computer science courses to their prerequisites.
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"},
}
//!-table
//!+main
func main() {
for i, course := range topoSort(prereqs) {
fmt.Printf("%d:\t%s\n", i+1, course)
}
}
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
}
//!-main