From a0d2e6f2853d3c9af6da9ff8be6748b1ad11e064 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?V=C3=ADtor=20Santos=20Costa?= <vsc@dcc.fc.up.pt>
Date: Thu, 22 Mar 2012 21:41:48 +0000
Subject: [PATCH] dgraph_leaves: all leaves in a directed graph (linear time).

---
 docs/yap.tex        |  7 +++++++
 library/dgraphs.yap | 11 +++++++++++
 2 files changed, 18 insertions(+)

diff --git a/docs/yap.tex b/docs/yap.tex
index 5709a446c..0d7ef8ea6 100644
--- a/docs/yap.tex
+++ b/docs/yap.tex
@@ -12635,6 +12635,13 @@ The path @var{Path} is a path starting at vertex @var{Vertex} in graph
 The path @var{Path} is a path starting at vertex @var{Vertex} in graph
 @var{Graph}.
 
+@item dgraph_leaves(+@var{Graph}, ?@var{Vertices})
+@findex  dgraph_leaves/2
+@snindex dgraph_leaves/2
+@cnindex dgraph_leaves/2
+The vertices @var{Vertices} have no outgoing edge in graph
+@var{Graph}.
+
 @end table
 
 @node UnDGraphs, Lambda , DGraphs, Library
diff --git a/library/dgraphs.yap b/library/dgraphs.yap
index 7dfb1d320..e081bc3bd 100644
--- a/library/dgraphs.yap
+++ b/library/dgraphs.yap
@@ -32,6 +32,7 @@
 	    dgraph_min_paths/3,
 	    dgraph_isomorphic/4,
 	    dgraph_path/3,
+	    dgraph_leaves/2,
 	    dgraph_reachable/3
 	]).
 
@@ -414,3 +415,13 @@ reachable([V|Vertices], Done0, DoneF, G, [V|EdgesF], Edges0) :-
 	rb_insert(Done0, V, [], Done1),
 	reachable(Kids, Done1, DoneI, G, EdgesF, EdgesI),
 	reachable(Vertices, DoneI, DoneF, G, EdgesI, Edges0).
+
+dgraph_leaves(Graph, Vertices) :-
+	rb_visit(Graph, Pairs),
+	vertices_without_children(Pairs, Vertices).
+
+vertices_without_children([], []).
+vertices_without_children((V-[]).Pairs, V.Vertices) :-
+	vertices_without_children(Pairs, Vertices).
+vertices_without_children(_V-[_|_].Pairs, Vertices) :-
+	vertices_without_children(Pairs, Vertices).