adjacency-list

问题 I have a pretty simple N:M relationship in SqlAlchemy 0.6.6. I have a class "attractLoop" that can contain a bunch of Media (Images or Videos). I need to have a list in which the same Media (let's say image) can be appended twice. The relationship is as follows: The media is a base class with most of the attributes Images and Videos will share. class BaseMedia(BaseClass.BaseClass, declarativeBase): __tablename__ = "base_media" _polymorphicIdentity = Column("polymorphic_identity", String(20),

问题 Initial scenario My software uses a tree data structure, and I store it in SQL. I use the abstraction called Adjacency List which consists of each row storing ID and ParentID . ID is Primary Key and ParentID is a Foreign Key to the same table. The problem I want to "convert" my SQL abstraction to Path Enumeration . It consists of each row storing ID and a varchar field storing the path of the IDs, from the root to the current row. For example, the Path field of the row with ID = 6 in this

问题 In my algorithms class I've been told that a draw back of Adjacency Lists for graph representation is the O(n) look up time for iterating through the array of adjacent nodes corresponding to each node. I implement my adjacency list by using a HashMap that maps nodes to a HashSet of their adjacent nodes, wouldn't that only take O(1) look up time? Is there something I'm missing? 回答1: As you know look up for value using key in HashMap is O(1). However, in adjacency list the value of the HashMap

问题 I have to prepare explanation of time complexity of removing vertex ( O(|V| + |E|) ) and edge ( O(|E|) ) in Adjency List. When removing vertex from graph with V vertices and E edges we need to go through all the edges ( O(|E|) ), of course, to check if which ones need to be removed with the vertex, but why do we need to check all vertices ? I don't understand why in order to remove edge we need to go through all the edges. I think I might have bad understanding from the beginning, so would

来源： https://stackoverflow.com/questions/20694742/determining-if-a-directed-graph-is-unilateral

来源： https://stackoverflow.com/questions/20694742/determining-if-a-directed-graph-is-unilateral

来源： https://stackoverflow.com/questions/20694742/determining-if-a-directed-graph-is-unilateral

来源： https://stackoverflow.com/questions/20694742/determining-if-a-directed-graph-is-unilateral

来源： https://stackoverflow.com/questions/20694742/determining-if-a-directed-graph-is-unilateral

问题 I am trying to generate a hierarchical tree object from a flat array with parent IDs. // `parent` represents an ID and not the nesting level. var flat = [ { id: 1, name: "Business", parent: 0 }, { id: 2, name: "Management", parent: 1 }, { id: 3, name: "Leadership", parent: 2 }, { id: 4, name: "Finance", parent: 1 }, { id: 5, name: "Fiction", parent: 0 }, { id: 6, name: "Accounting", parent: 1 }, { id: 7, name: "Project Management", parent: 2 } ]; The final tree object should look as follows: