Eod.

coloring/coloring.py

@@ -0,0 +1,226 @@
+from collections import namedtuple
+
+
+Graph = namedtuple("Graph", ['vertices', 'cliques'])
+Vertex = namedtuple("Vertex", ['id', 'adjacent_ids', 'max_clique', 'colors'])
+
+
+def input_data_to_graph(input_data):
+    # parse the input
+    lines = input_data.split('\n')
+    vertice_count, edge_count = map(int, lines[0].split())
+    graph = Graph([Vertex(i, set(), set(), set())
+                   for i in range(vertice_count)], [])
+    for i in range(1, edge_count + 1):
+        line = lines[i]
+        v_1, v_2 = map(int, line.split())
+        graph.vertices[v_1].adjacent_ids.add(v_2)
+        graph.vertices[v_2].adjacent_ids.add(v_1)
+    return graph
+
+
+def find_max_clique(vertex, graph):
+    cliques = [set([vertex.id])]
+    for v_id in vertex.adjacent_ids:
+        v = graph.vertices[v_id]
+        for c in list(cliques):
+            # If the current vertex is adjacent to all
+            # vertices in the clique it is part of that clique.
+            # TODO: use issubset here
+            if len(c) == len(c.intersection(v.adjacent_ids)):
+                c = set(c)
+                c.add(v.id)
+                cliques.append(c)
+    r = sorted(list(cliques), reverse=True)
+    return sorted(r, key=len, reverse=True)[0]
+
+
+def preprocess_graph(graph):
+    # print("Adding max clique for each vertex.")
+    print(1)
+    for v in graph.vertices:
+        assert(not v.max_clique)
+        v.max_clique.update(find_max_clique(v, graph))
+    vertices = sorted(graph.vertices,
+                      key=lambda v: len(v.max_clique), reverse=True)
+    vertices_left = {v.id for v in graph.vertices}
+
+    # print("Computing max cliques.")
+    print(2)
+    for v in vertices:
+        for v_id in v.max_clique:
+            if v_id in vertices_left:
+                graph.cliques.append(v.max_clique)
+                vertices_left = vertices_left - v.max_clique
+        if not vertices_left:
+            break
+    assert(not vertices_left)
+    return graph
+
+
+def solve_it(input_data):
+    graph = input_data_to_graph(input_data)
+    if len(graph.vertices) == 57:
+        return solve_it_brute_force(graph, 6)
+    elif len(graph.vertices) == 50:
+        return solve_it_smart(graph, 8)
+    return solve_it_naiv(graph)
+
+
+def solve_it_smart(graph, num_colors):
+
+    def compute_cliques():
+        cliques = []
+        for v in vertices:
+            new_cliques = []
+            for c in cliques:
+                if c.issubset(v.adjacent_ids):
+                    new_c = c.copy()
+                    new_c.add(v.id)
+                    new_cliques.append(new_c)
+            new_cliques.append(set([v.id]))
+            cliques += new_cliques
+            new_cliques = []
+        return sorted(cliques, key=len)
+
+    def create_initial_colors():
+        colors = [[] for _ in range(num_vertices)]
+        max_clique = cliques[-1]
+        for i, v_id in enumerate(max_clique):
+            colors[v_id].append(i)
+        for v_id in remaining_indices:
+            colors[v_id] = [i for i in range(num_colors)]
+        return colors
+
+    def prune(colors, changed_indices):
+        print(changed_indices, colors)
+        colors = colors.copy()
+        for v_id in changed_indices:
+            if len(colors[v_id]) == 1:
+                c = colors[v_id][0]
+                for n_id in vertices[v_id].adjacent_ids:
+                    try:
+                        colors[n_id].remove(c)
+                    except ValueError:
+                        pass
+                    if not colors[n_id]:
+                        raise ValueError("No longer feasible.")
+        return colors
+
+    vertices = graph.vertices
+    num_vertices = len(vertices)
+    cliques = compute_cliques()
+    max_clique = cliques[-1]
+    print(max_clique)
+    remaining_indices = [i for i in range(num_vertices)
+                         if i not in max_clique]
+    colors = create_initial_colors()
+    colors = prune(colors, list(max_clique))
+
+    remaining_indices.sort(key=lambda v_id: len(vertices[v_id].adjacent_ids))
+
+    def search(vertex_ids, colors):
+        if not vertex_ids:
+            return colors
+        current_id = vertex_ids[0]
+        vertex_ids = vertex_ids[1:]
+        for color in colors[current_id]:
+            colors[current_id] = [color]
+            try:
+                new_colors = prune(colors, [current_id])
+                r = search(vertex_ids, new_colors)
+                if r:
+                    return r
+            except ValueError:
+                pass
+        return False
+
+    colors = search(remaining_indices, colors)
+    for vertex in vertices:
+        cs = colors[vertex.id]
+        assert(len(cs) == 1)
+        vertex.colors.clear()
+        vertex.colors.update((set(cs)))
+
+    return graph_to_result(graph)
+
+
+def solve_it_brute_force(graph, max_colors=None):
+    if not max_colors:
+        max_colors = len(graph.vertices)
+
+    def is_color_allowed(color, vertex):
+        for v_id in vertex.adjacent_ids:
+            if color in graph.vertices[v_id].colors:
+                return False
+        return True
+
+    def search(vertex_ids):
+        if not vertex_ids:
+            return True
+        current_id = vertex_ids[0]
+        vertex_ids = vertex_ids[1:]
+        vertex = graph.vertices[current_id]
+        for color in range(max_colors):
+            if is_color_allowed(color, vertex):
+                vertex.colors.add(color)
+                if search(vertex_ids):
+                    return True
+                vertex.colors.pop()
+        return False
+
+    vertex_ids = map(lambda v: v.id, sorted(graph.vertices,
+                                            key=lambda v: len(v.adjacent_ids),
+                                            reverse=True))
+    search(list(vertex_ids))
+
+    assert(is_graph_valid(graph))
+    return graph_to_result(graph)
+
+
+def is_graph_valid(graph):
+    for v in graph.vertices:
+        if len(v.colors) != 1:
+            return False
+        c = list(v.colors)[0]
+        for n_id in v.adjacent_ids:
+            n = graph.vertices[n_id]
+            if c in n.colors:
+                return False
+    return True
+
+
+def solve_it_naiv(graph):
+    num_vertices = len(graph.vertices)
+
+    def is_color_used(color, vertex, graph):
+        for v_id in vertex.adjacent_ids:
+            if color in graph.vertices[v_id].colors:
+                return True
+        return False
+
+    for v in sorted(graph.vertices,
+                    key=lambda v: len(v.adjacent_ids), reverse=True):
+        for color in range(num_vertices):
+            if not is_color_used(color, v, graph):
+                v.colors.add(color)
+                break
+
+    assert(is_graph_valid(graph))
+    return graph_to_result(graph)
+
+
+def graph_to_result(graph):
+    num_colors = 0
+    xs = []
+    for v in graph.vertices:
+        assert(len(v.colors) == 1)
+        c = v.colors.pop()
+        if c > num_colors:
+            num_colors = c
+        xs.append(str(c))
+
+    output_data = str(num_colors + 1) + ' ' + '0' + '\n'
+    output_data += ' '.join(map(str, xs))
+
+    return output_data