iframe-proxy | Sunbelt Computer Software

134 lines (112 loc) · 5.63 KB
# From Classic Computer Science Problems in Python Chapter 4
# Copyright 2018 David Kopec
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from typing import TypeVar, Generic, List, Optional
from edge import Edge
V = TypeVar('V') # type of the vertices in the graph
class Graph(Generic[V]):
    def __init__(self, vertices: List[V] = []) -> None:
        self._vertices: List[V] = vertices
        self._edges: List[List[Edge]] = [[] for _ in vertices]
    @property
    def vertex_count(self) -> int:
        return len(self._vertices) # Number of vertices
    @property
    def edge_count(self) -> int:
        return sum(map(len, self._edges)) # Number of edges
    # Add a vertex to the graph and return its index
    def add_vertex(self, vertex: V) -> int:
        self._vertices.append(vertex)
        self._edges.append([]) # add empty list for containing edges
        return self.vertex_count - 1 # return index of added vertex
    # This is an undirected graph,
    # so we always add edges in both directions
    def add_edge(self, edge: Edge) -> None:
        self._edges[edge.u].append(edge)
        self._edges[edge.v].append(edge.reversed())
    # Add an edge using vertex indices (convenience method)
    def add_edge_by_indices(self, u: int, v: int) -> None:
        edge: Edge = Edge(u, v)
        self.add_edge(edge)
    # Add an edge by looking up vertex indices (convenience method)
    def add_edge_by_vertices(self, first: V, second: V) -> None:
        u: int = self._vertices.index(first)
        v: int = self._vertices.index(second)
        self.add_edge_by_indices(u, v)
    # Find the vertex at a specific index
    def vertex_at(self, index: int) -> V:
        return self._vertices[index]
    # Find the index of a vertex in the graph
    def index_of(self, vertex: V) -> int:
        return self._vertices.index(vertex)
    # Find the vertices that a vertex at some index is connected to
    def neighbors_for_index(self, index: int) -> List[V]:
        return list(map(self.vertex_at, [e.v for e in self._edges[index]]))
    # Lookup a vertice's index and find its neighbors (convenience method)
    def neighbors_for_vertex(self, vertex: V) -> List[V]:
        return self.neighbors_for_index(self.index_of(vertex))
    # Return all of the edges associated with a vertex at some index
    def edges_for_index(self, index: int) -> List[Edge]:
        return self._edges[index]
    # Lookup the index of a vertex and return its edges (convenience method)
    def edges_for_vertex(self, vertex: V) -> List[Edge]:
        return self.edges_for_index(self.index_of(vertex))
    # Make it easy to pretty-print a Graph
    def __str__(self) -> str:
        desc: str = ""
        for i in range(self.vertex_count):
            desc += f"{self.vertex_at(i)} -> {self.neighbors_for_index(i)}\n"
        return desc
if __name__ == "__main__":
    # test basic Graph construction
    city_graph: Graph[str] = Graph(["Seattle", "San Francisco", "Los Angeles", "Riverside", "Phoenix", "Chicago", "Boston", "New York", "Atlanta", "Miami", "Dallas", "Houston", "Detroit", "Philadelphia", "Washington"])
    city_graph.add_edge_by_vertices("Seattle", "Chicago")
    city_graph.add_edge_by_vertices("Seattle", "San Francisco")
    city_graph.add_edge_by_vertices("San Francisco", "Riverside")
    city_graph.add_edge_by_vertices("San Francisco", "Los Angeles")
    city_graph.add_edge_by_vertices("Los Angeles", "Riverside")
    city_graph.add_edge_by_vertices("Los Angeles", "Phoenix")
    city_graph.add_edge_by_vertices("Riverside", "Phoenix")
    city_graph.add_edge_by_vertices("Riverside", "Chicago")
    city_graph.add_edge_by_vertices("Phoenix", "Dallas")
    city_graph.add_edge_by_vertices("Phoenix", "Houston")
    city_graph.add_edge_by_vertices("Dallas", "Chicago")
    city_graph.add_edge_by_vertices("Dallas", "Atlanta")
    city_graph.add_edge_by_vertices("Dallas", "Houston")
    city_graph.add_edge_by_vertices("Houston", "Atlanta")
    city_graph.add_edge_by_vertices("Houston", "Miami")
    city_graph.add_edge_by_vertices("Atlanta", "Chicago")
    city_graph.add_edge_by_vertices("Atlanta", "Washington")
    city_graph.add_edge_by_vertices("Atlanta", "Miami")
    city_graph.add_edge_by_vertices("Miami", "Washington")
    city_graph.add_edge_by_vertices("Chicago", "Detroit")
    city_graph.add_edge_by_vertices("Detroit", "Boston")
    city_graph.add_edge_by_vertices("Detroit", "Washington")
    city_graph.add_edge_by_vertices("Detroit", "New York")
    city_graph.add_edge_by_vertices("Boston", "New York")
    city_graph.add_edge_by_vertices("New York", "Philadelphia")
    city_graph.add_edge_by_vertices("Philadelphia", "Washington")
    print(city_graph)
    # Reuse BFS from Chapter 2 on city_graph
    import sys
    sys.path.insert(0, '..') # so we can access the Chapter2 package in the parent directory
    from Chapter2.generic_search import bfs, Node, node_to_path
    bfs_result: Optional[Node[V]] = bfs("Boston", lambda x: x == "Miami", city_graph.neighbors_for_vertex)
    if bfs_result is None:
        print("No solution found using breadth-first search!")
        path: List[V] = node_to_path(bfs_result)
        print("Path from Boston to Miami:")
        print(path)
Sunbelt Computer Software

PL/B Language Development and Support

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Sunbelt Computer Software

PL/B Language Development and Support

FilesExpand file tree

graph.py

Latest commit

History

graph.py

File metadata and controls
