Add Kahn's algorithm to graph.h #1089
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src/util/graph.h
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| @@ -19,6 +19,9 @@ Author: Daniel Kroening, [email protected] | |||
| #include <ostream> | |||
| #include <cassert> | |||
| #include <algorithm> | |||
| #include <queue> | |||
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| #include <util/invariant.h> | |||
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Nit picking: in util we just use #include "invariant.h"
src/util/graph.h
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| } | ||
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| // if no edge is left in the graph, it is acyclic | ||
| bool is_dag=none_of( |
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Doesn't this need a std:: ?
src/util/graph.h
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| @@ -226,6 +229,12 @@ class grapht | |||
| // return value: number of SCCs | |||
| std::size_t SCCs(std::vector<node_indext> &subgraph_nr); | |||
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| bool is_dag() | |||
src/util/graph.h
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| { | ||
| return size()==0 || !topsort().empty(); | ||
| } | ||
| std::list<node_indext> topsort(); |
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Should be marked const (plus add a blank line in between)
src/util/graph.h
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| @@ -226,6 +229,12 @@ class grapht | |||
| // return value: number of SCCs | |||
| std::size_t SCCs(std::vector<node_indext> &subgraph_nr); | |||
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| bool is_dag() | |||
| { | |||
| return size()==0 || !topsort().empty(); | |||
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I believe we've now got empty()
src/util/graph.h
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| { | ||
| std::list<node_indext> nodelist; | ||
| std::queue<node_indext> indeg0_nodes; | ||
| std::map<node_indext, size_t> in_deg; |
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I would recommend using a zero-initialised std::vector of size nodes.size()
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ok, changed this, but then we assume node_indext to be an integral value
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I believe this is a reasonable (likely necessary) assumption.
src/util/graph.h
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| for(const auto &edge : out(source)) | ||
| { | ||
| const node_indext target=edge.first; | ||
| INVARIANT(in_deg[target]!=0, "In-degree of node cannot be 0."); |
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Nit picking/question: with throw we even have a lint check that the message does not start with an uppercase character; should the same apply to invariants?
src/util/graph.h
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| bool is_dag=none_of( | ||
| in_deg.begin(), | ||
| in_deg.end(), | ||
| [](std::pair<node_indext, size_t> p) { return p.second>0; }); |
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Wouldn't bool is_dag=nodelist.size()==nodes.size(); also do the trick?
mgudemann
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@tautschnig thank you for the comments, I have adapted the PR |
src/util/graph.h
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| bool is_dag=(nodelist.size()==nodes.size()); | ||
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| // return empty list in case of cyclic graph | ||
| if(!is_dag) |
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Nit picking: you might now get rid of the is_dag temporary and use if(nodelist.size()!=nodes.size())
mgudemann
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@tautschnig thanks, I have simplified the |
This adds topological sorting to
graph.h.