It depends on the problem. Adjacency Matrix Uses O(n^2) memory It is fast to lookup and check for presence or absence of a specific edge between any two nodes O(1) It is slow to iterate over all edges It is slow to add/delete a node; a complex operation O(n^2) It is fast to add a … Read more
Assuming: edges = [(‘a’, ‘b’), (‘a’, ‘b’), (‘a’, ‘c’)] Here’s some code for the matrix: from collections import defaultdict matrix = defaultdict(int) for edge in edges: matrix[edge] += 1 print matrix[‘a’, ‘b’] 2 And for the “list”: from collections import defaultdict adj_list = defaultdict(lambda: defaultdict(lambda: 0)) for start, end in edges: adj_list[start][end] += 1 print … Read more
Unfortunately MySQL doesn’t support CTE (Common Table Expressions). This is long overdue IMO. Often, you can just use a subquery instead, but this particular CTE is recursive: it refers to itself inside the query. Recursive CTE’s are extremely useful for hierarchical data, but again: MySql doesn’t support them at all. You have to implement a … Read more