Move tour, LOG and LOGN in utils, add vertices_from_set

utils.py

@@ -1,4 +1,20 @@
 
+import sys
+
+def LOG( *args ):
+    """Print something on stderr and flush"""
+    for msg in args:
+        sys.stderr.write( str(msg) )
+        sys.stderr.write(" ")
+        sys.stderr.flush()
+
+
+def LOGN( *args ):
+    """Print something on stdeer, with a trailing new line, and flush"""
+    LOG( *args )
+    LOG("\n")
+
+
 def adjacency_from_set( segments ):
     graph = {}
     for start,end in segments:
@@ -8,3 +24,17 @@ def adjacency_from_set( segments ):
         graph[end].append( start )
     return graph
 
+
+def vertices_from_set( segments ):
+    vertices = set()
+    for start,end in segments:
+        vertices.add(start)
+        vertices.add(end)
+    return vertices
+
+
+def tour(lst):
+    # consecutive pairs in lst  + last-to-first element
+    for a,b in zip(lst, lst[1:] + [lst[0]]):
+        yield (a,b)
+