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70 lines
1.4 KiB
Go
70 lines
1.4 KiB
Go
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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// See page 136.
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// The toposort program prints the nodes of a DAG in topological order.
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package main
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import (
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"fmt"
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"sort"
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)
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//!+table
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// prereqs maps computer science courses to their prerequisites.
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var prereqs = map[string][]string{
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"algorithms": {"data structures"},
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"calculus": {"linear algebra"},
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"compilers": {
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"data structures",
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"formal languages",
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"computer organization",
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},
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"data structures": {"discrete math"},
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"databases": {"data structures"},
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"discrete math": {"intro to programming"},
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"formal languages": {"discrete math"},
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"networks": {"operating systems"},
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"operating systems": {"data structures", "computer organization"},
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"programming languages": {"data structures", "computer organization"},
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}
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//!-table
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//!+main
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func main() {
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for i, course := range topoSort(prereqs) {
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fmt.Printf("%d:\t%s\n", i+1, course)
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}
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}
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func topoSort(m map[string][]string) []string {
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var order []string
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seen := make(map[string]bool)
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var visitAll func(items []string)
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visitAll = func(items []string) {
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for _, item := range items {
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if !seen[item] {
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seen[item] = true
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visitAll(m[item])
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order = append(order, item)
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}
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}
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}
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var keys []string
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for key := range m {
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keys = append(keys, key)
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}
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sort.Strings(keys)
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visitAll(keys)
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return order
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}
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//!-main
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