Data commit

Task/Graph-colouring/Python/graph-colouring.py

@@ -0,0 +1,73 @@
+import re
+from collections import defaultdict
+from itertools import count
+
+
+connection_re = r"""
+    (?: (?P<N1>\d+) - (?P<N2>\d+) | (?P<N>\d+) (?!\s*-))
+    """
+
+class Graph:
+
+    def __init__(self, name, connections):
+        self.name = name
+        self.connections = connections
+        g = self.graph = defaultdict(list)  # maps vertex to direct connections
+
+        matches = re.finditer(connection_re, connections,
+                              re.MULTILINE | re.VERBOSE)
+        for match in matches:
+            n1, n2, n = match.groups()
+            if n:
+                g[n] += []
+            else:
+                g[n1].append(n2)    # Each the neighbour of the other
+                g[n2].append(n1)
+
+    def greedy_colour(self, order=None):
+        "Greedy colourisation algo."
+        if order is None:
+            order = self.graph      # Choose something
+        colour = self.colour = {}
+        neighbours = self.graph
+        for node in order:
+            used_neighbour_colours = (colour[nbr] for nbr in neighbours[node]
+                                      if nbr in colour)
+            colour[node] = first_avail_int(used_neighbour_colours)
+        self.pp_colours()
+        return colour
+
+    def pp_colours(self):
+        print(f"\n{self.name}")
+        c = self.colour
+        e = canonical_edges = set()
+        for n1, neighbours in sorted(self.graph.items()):
+            if neighbours:
+                for n2 in neighbours:
+                    edge = tuple(sorted([n1, n2]))
+                    if edge not in canonical_edges:
+                        print(f"       {n1}-{n2}: Colour: {c[n1]}, {c[n2]}")
+                        canonical_edges.add(edge)
+            else:
+                print(f"         {n1}: Colour: {c[n1]}")
+        lc = len(set(c.values()))
+        print(f"    #Nodes: {len(c)}\n    #Edges: {len(e)}\n  #Colours: {lc}")
+
+
+def first_avail_int(data):
+    "return lowest int 0... not in data"
+    d = set(data)
+    for i in count():
+        if i not in d:
+            return i
+
+
+if __name__ == '__main__':
+    for name, connections in [
+            ('Ex1', "0-1 1-2 2-0 3"),
+            ('Ex2', "1-6 1-7 1-8 2-5 2-7 2-8 3-5 3-6 3-8 4-5 4-6 4-7"),
+            ('Ex3', "1-4 1-6 1-8 3-2 3-6 3-8 5-2 5-4 5-8 7-2 7-4 7-6"),
+            ('Ex4', "1-6 7-1 8-1 5-2 2-7 2-8 3-5 6-3 3-8 4-5 4-6 4-7"),
+            ]:
+        g = Graph(name, connections)
+        g.greedy_colour()