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* Retranslate the complete English edition from Simplified Chinese * Polish three English explanations after reader-focused review
117 lines
3.8 KiB
Python
117 lines
3.8 KiB
Python
"""
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File: graph_adjacency_matrix.py
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Created Time: 2023-02-23
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Author: krahets (krahets@163.com)
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"""
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import sys
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from pathlib import Path
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sys.path.append(str(Path(__file__).parent.parent))
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from modules import Vertex, print_matrix
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class GraphAdjMat:
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"""Undirected graph class implemented with an adjacency matrix"""
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def __init__(self, vertices: list[int], edges: list[list[int]]):
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"""Constructor"""
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# Vertex list: elements are vertex values, and indices are vertex indices
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self.vertices: list[int] = []
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# Adjacency matrix: row and column indices correspond to vertex indices
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self.adj_mat: list[list[int]] = []
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# Add a vertex
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for val in vertices:
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self.add_vertex(val)
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# Add an edge
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# Note that the entries in edges are vertex indices, corresponding to element indices in vertices
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for e in edges:
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self.add_edge(e[0], e[1])
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def size(self) -> int:
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"""Get the number of vertices"""
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return len(self.vertices)
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def add_vertex(self, val: int):
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"""Add a vertex"""
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n = self.size()
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# Append the new vertex value to the vertex list
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self.vertices.append(val)
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# Add a row to the adjacency matrix
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new_row = [0] * n
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self.adj_mat.append(new_row)
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# Add a column to the adjacency matrix
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for row in self.adj_mat:
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row.append(0)
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def remove_vertex(self, index: int):
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"""Remove a vertex"""
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if index >= self.size():
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raise IndexError()
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# Remove the vertex at index `index` from the vertex list
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self.vertices.pop(index)
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# Remove row `index` from the adjacency matrix
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self.adj_mat.pop(index)
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# Remove column `index` from the adjacency matrix
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for row in self.adj_mat:
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row.pop(index)
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def add_edge(self, i: int, j: int):
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"""Add an edge"""
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# Parameters i and j are element indices in vertices
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# Handle out-of-bounds or equal indices
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if i < 0 or j < 0 or i >= self.size() or j >= self.size() or i == j:
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raise IndexError()
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# For an undirected graph, the adjacency matrix is symmetric about its main diagonal: entries (i, j) and (j, i) are equal
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self.adj_mat[i][j] = 1
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self.adj_mat[j][i] = 1
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def remove_edge(self, i: int, j: int):
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"""Remove an edge"""
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# Parameters i and j are element indices in vertices
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# Handle out-of-bounds or equal indices
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if i < 0 or j < 0 or i >= self.size() or j >= self.size() or i == j:
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raise IndexError()
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self.adj_mat[i][j] = 0
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self.adj_mat[j][i] = 0
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def print(self):
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"""Print the adjacency matrix"""
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print("Vertex list =", self.vertices)
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print("Adjacency matrix =")
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print_matrix(self.adj_mat)
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"""Driver code"""
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if __name__ == "__main__":
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# Initialize the undirected graph
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# Note that the entries in edges are vertex indices, corresponding to element indices in vertices
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vertices = [1, 3, 2, 5, 4]
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edges = [[0, 1], [0, 3], [1, 2], [2, 3], [2, 4], [3, 4]]
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graph = GraphAdjMat(vertices, edges)
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print("\nGraph after initialization:")
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graph.print()
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# Add an edge
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# Vertices 1 and 2 have indices 0 and 2, respectively
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graph.add_edge(0, 2)
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print("\nGraph after adding edge 1-2:")
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graph.print()
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# Remove an edge
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# Vertices 1 and 3 have indices 0 and 1, respectively
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graph.remove_edge(0, 1)
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print("\nGraph after removing edge 1-3:")
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graph.print()
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# Add a vertex
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graph.add_vertex(6)
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print("\nGraph after adding vertex 6:")
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graph.print()
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# Remove a vertex
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# Vertex 3 has index 1
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graph.remove_vertex(1)
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print("\nGraph after removing vertex 3:")
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graph.print()
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