mirror of https://github.com/deuill/grawkit.git
73 lines
1.4 KiB
Go
73 lines
1.4 KiB
Go
// Topological sorting
|
|
|
|
package parser
|
|
|
|
/*
|
|
This algorithm is taken from:
|
|
https://en.wikipedia.org/wiki/Topological_sorting#Depth-first_search
|
|
|
|
L ← Empty list that will contain the sorted nodes
|
|
while exists nodes without a permanent mark do
|
|
select an unmarked node n
|
|
visit(n)
|
|
|
|
function visit(node n)
|
|
if n has a permanent mark then
|
|
return
|
|
if n has a temporary mark then
|
|
stop (not a DAG)
|
|
|
|
mark n with a temporary mark
|
|
|
|
for each node m with an edge from n to m do
|
|
visit(m)
|
|
|
|
remove temporary mark from n
|
|
mark n with a permanent mark
|
|
add n to head of L
|
|
*/
|
|
|
|
// Perform a topological sort on the given graph.
|
|
func topoSort(graph map[string]map[string]struct{}) []string {
|
|
if len(graph) == 0 {
|
|
return nil
|
|
}
|
|
|
|
unmarked := make(map[string]struct{})
|
|
for node := range graph {
|
|
unmarked[node] = struct{}{}
|
|
}
|
|
permMarks := make(map[string]struct{})
|
|
tempMarks := make(map[string]struct{})
|
|
var sorted []string
|
|
|
|
var visit func(string)
|
|
visit = func(n string) {
|
|
if _, ok := permMarks[n]; ok {
|
|
return
|
|
}
|
|
if _, ok := tempMarks[n]; ok {
|
|
return
|
|
}
|
|
tempMarks[n] = struct{}{}
|
|
for m := range graph[n] {
|
|
visit(m)
|
|
}
|
|
delete(tempMarks, n)
|
|
permMarks[n] = struct{}{}
|
|
delete(unmarked, n)
|
|
sorted = append(sorted, n)
|
|
return
|
|
}
|
|
|
|
for len(unmarked) > 0 {
|
|
var n string
|
|
for n = range unmarked {
|
|
break
|
|
}
|
|
visit(n)
|
|
}
|
|
|
|
return sorted
|
|
}
|