完成以下代码：""" File: fromexample.py Project 12.9 Defines and tests the all pairs shortest paths algorithm of Floyd. Uses the graph from Figure 12.19 of the text, as represented in the file example.txt. """ from graph import LinkedDirectedGraph import random from arrays import Array # Functions for working with infinity def isLessWithInfinity(a, b): """Returns False if a == b or a == INFINITY and b != INFINITY. Otherwise, returns True if b == INFINITY or returns a < b.""" if a == LinkedDirectedGraph.INFINITY and b == LinkedDirectedGraph.INFINITY: return False elif b == LinkedDirectedGraph.INFINITY: return True elif a == LinkedDirectedGraph.INFINITY: return False else: return a < b def addWithInfinity(a, b): """If a == INFINITY or b == INFINITY, returns INFINITY. Otherwise, returns a + b.""" if a == LinkedDirectedGraph.INFINITY or b == LinkedDirectedGraph.INFINITY: return LinkedDirectedGraph.INFINITY else: return a + b def minDistance(a, b): if isLessWithInfinity(a, b): return a else: return b # Define a function that uses Floyd's algorithm def allPairsShortestPaths(matrix): """ please complete the Floyd algorithm here """ pass # Define a function to print a labeled distance matrix def printDistanceMatrix(matrix, table): """Prints the distance matrix with rows and columns labels with the index positions and vertex labels.""" labels = Array(len(table)) index = 0 labelWidth = 0 indexWidth = 0 for label in table: labels[table[label]] = label labelWidth = max(labelWidth, len(str(label))) indexWidth = max(indexWidth, len(str(index))) index += 1 weightWidth = 0 for row in range(matrix.getHeight()): for column in range(matrix.getWidth()): weightWidth = max(weightWidth, len(str(matrix[row][column]))) weightWidth = max(weightWidth, labelWidth, indexWidth) topRowLeftMargin

以下是完成代码的步骤：
1. 导入所需的模块及类。代码中需要使用LinkedDirectedGraph类和Array类，因此需要导入graph和arrays模块。
2. 创建一个LinkedDirectedGraph对象，并读取文件example.txt中的图数据，将其添加到图中。
3. 实现Floyd算法，计算所有节点对之间的最短路径，将结果保存到一个二维数组中。
4. 输出结果数组，展示所有节点对之间的最短路径。