Adjacency List Puns

The following is mentioned in Wiki:

>The main operation performed by the adjacency list data structure is to report a list of the neighbors of a given vertex. Using any of the implementations detailed above, this can be performed in constant time per neighbor. In other words, the total time to report all of the neighbors of a vertex v is proportional to the degree of v

Why is it O(deg(v)) instead of O(1)? Can't we just directly access the list associated with a particular vertex?

Hi everyone, I am struggling to make a query for the M-M relations in DynamoDB

in this answer u/F_SO_K provided a great example:

https://preview.redd.it/bmutilqhv6s71.png?width=1380&format=png&auto=webp&s=aa38d7a3f4f7ff2fadcbb83cbf9e2266f5d66a62

​1) here I can retrieve all actors by Movie8, but how can I retrieve Actor1's all movies with a single query?

2. what if Moview8 has multiple Actors should I duplicate the movie row for each Actor with the same movie data?

DOI: 10.1142/s0217979221501861

URL: https://www.worldscientific.com/doi/abs/10.1142/S0217979221501861

Adjacency matrix can give constant time lookup for edges and the tradeoff of space. However, in an adjacency list representation, why don't we a map of <vertex, set of vertices> for the graph instead of list<list> data structure? Doing it the alternative way would still give us lookup for edges in constant time, and be dense as well.

Hey guys, I’m trying to create an adjacency list class that let’s me add vertices, edges, print etc.

The problem I’m facing is that I cannot use Java.utils and all examples online use it. Is there a work around or a good article/video explaining it ?

If anyone could explain it to me or link a good explanation that would be super helpful.

I'm trying to count all paths between 2 nodes in a directed graph. The graph may be cyclic however, I want to avoid return back to the source node -- thus avoiding infinite loops. The adjacency lists are defined as follows:

adjlist = {{ 1, 2 },{ 0, 3 },{ 0, 3 },{ 1, 2 },}   

meaning that node 0 (first in list) can connect to nodes 1 and 2, node 1 can connect to nodes 0 and 3, node 2 can connect to nodes 0 and 3, and node 3 can connect to nodes 1 and 2.

I have tried this:

public int numPaths(int[][] adjlist, int src, int dst) {   
// TODO  
int paths = 0;   
for (int i = 0; i < adjlist[src].length; i++) {           
    boolean[] visited = new boolean[adjlist.length];           
    visited[src] = true;           
    DFS2(adjlist, adjlist[src][i], dst, paths, visited);    
 }    
 return paths;  
}    

public static void DFS2(int[][] adjlist, int src, int dst, int paths, boolean[] visited) {  
visited[src] = true;   
if (src == dst) {           
    paths++;   
}   
else {           
    for (int i = 0; i < adjlist[src].length; i++) {                   
        if (visited[i] == false) {                           
            DFS2(adjlist, adjlist[src][i], dst, paths, visited);                   
        }               
     }   
}  

}

I am using DFS however im getting the following error:

Exception in thread "main" java.lang.StackOverflowError  

Meaning I'm getting an infinite recursion. Any help would be great, thanks.

How is possible to convert an adjacency matrix to an edge list ? I know that i can declare the matrix like this

int i,j,n;
   printf("Enter number of vertices:");
   scanf("%d", &n);
   printf("\nEnter the adjacency matrix:\n");
    for (i = 0; i < n; i++)
       for (j = 0; j < n; j++)
          scanf("%d", &G[i][j]);

but how to convert it ?

(link for reference: https://github.com/malwaredllc/semantic-viz)

I'm trying to figure out how to convert an undirected graph (currently represented as an adjacency list using Data.Map) to a graph (Data.Graph).

It seems one way would be to extract edges from the map like so:

From the hash map:

[("cat",["wildcat","domestic"]), ...]

the edges would be:

[("cat", "domestic"), ("cat","wildcat"), ...]

However, looking at the Edge data type in Data.Graph, it seems it's defined as:

type Edge = (Vertex, Vertex)

and Vertexes are defined as:

type Vertex = Int

which is problematic, because my data consists of strings, not integers.

Basically, my end goal here is to visualize the graph using Haskell (was thinking of using graphviz) instead of pawning it off to Python/Matplotlib.

Any advice on the best strategy to achieve this would be greatly appreciated!

For the current project that I'm working on, I have to store translations of words from one language to another. The operation on this data which I will most commonly need to perform is getting translations with respect to a word.

My idea has been to store this in a graph-like format, in which every word would be a node and would have edges pointing towards possible translations of the word into another language.

I have looked around to see what might be the best package to use for this and my current thoughts are that it would be best to use `Data.IntMap`, where each key is the id for a specific word in a specific language and each value stores the word and an adjacency list of ids which are translations for that word in another language. My understanding is that this would allow for logarithmic time complexity when looking up words and therefore logarithmic time complexity for retrieving the list of translations for a given word.

Does this sound like a reasonable way of storing this data? It feels slightly `wrong`, as I do not think that it should be required for me to write code which manages the adjacency lists of the different 'nodes' of the 'graphs', but I have not yet found a graph library which allows for logarithmic or better lookup.

Any help would be appreciated!

#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <map>

struct Vertex
{
    std::string name;
    Vertex(std::string name)
        : name(name) {}
};

class AdjacencyList
{
private:
    //adjacency list
    std::vector<std::pair<int, std::list<int>>> mAdj;
    //map of ids for each Vertex
    std::map<std::string, int> mIDs;

public:
    void addVertex(const Vertex& vertex)
    {
        int id = mIDs.size();
        mIDs.insert(std::make_pair(vertex.name, id));
        std::list<int> ver;
        mAdj.push_back(std::make_pair(id, ver));
    }

    void addEdge (int id1, int id2)
    {
        mAdj[id1].second.push_back(id2);
    }

    void addEdge (std::string name1, std::string name2)
    {
        int id1 = mIDs[name1];
        int id2 = mIDs[name2];
        addEdge(id1, id2);
    }
    // void addEdge (const Vertex& ver1 ........ you get the idea
    
    void printAdjList()
    {
        for (auto i : mAdj)
        {
            int id = i.first;
            std::cout << "ID: " << id << "| " << id << " -> ";
            for (auto j : i.second)
            {
                std::cout << j << " -> ";
            }
            std::cout << "\n";
        }
    }
};

int main()
{
    
    std::vector<Vertex> vertices;
    AdjacencyList adj_list;

    //init vertices
    for (int i = 0; i < 4; i++)
    {
        Vertex ver("vertex" + std::to_string(i));
        adj_list.addVertex(ver);
    }
    
    //add edges
    adj_list.addEdge(2, 4);
    adj_list.addEdge("vertex3", "vertex0");
    adj_list.addEdge("vertex3", "vertex1");

    adj_list.printAdjList();

}

output in this example:

ID: 0| 0 ->
ID: 1| 1 ->
ID: 2| 2 -> 4 ->
ID: 3| 3 -> 0 -> 1 ->

I'm sure there's a more efficient way to do this. my knowledge in C++ is still limited and I would like a review of this code with suggestions on ways to improve if it's not too much of a bother.

thanks in advance for anyone who helps

Just started learning about graph and it's various representations (matrix and adjacency list). Now I found that the adjacency list representation can be implemented in various ways:

1. Array of arrays (where we have one index in main array for each vertices and adjacent vertices are in subarrays at each of this index)
2. Array of linked lists (most common implementation I have seen)
3. Map of array (same as array of arrays, except that outer array is now a Map)

Was wondering why would I prefer one of these implementation over the other. Is one implementation more common or efficient in any way or they all the same?

For interviews, does it matter which representation you use to solve graph problems? Are there certain cases where it is more efficient / simpler to use one over the other?

Hello All,
First Post. I'm a beginner to python and data structures in general. My question is regarding the implementation of the graph adjacency list using linked lists in python! Basically, I was working on the code from geeks for geeks on adjacency lists:

""" A Python program to demonstrate the adjacency list representation of the graph """
# A class to represent the adjacency list of the node 


class AdjNode:
    def __init__(self, data):
        self.vertex = data
        self.next = None

# A class to represent a graph. A graph is the list of the adjacency lists. Size of the array will be the no. of the vertices "V" 

class Graph:
    def __init__(self, vertices):
        self.V = vertices
        self.graph = [None] * self.V

# Function to add an edge in an undirected graph  

    def add_edge(self, src, dest): # Adding the node to the source node
        node = AdjNode(dest)
        node.next = self.graph[src] #Please explain
        self.graph[src] = node #Please explain

# Adding the source node to the destination as it is the undirected graph

        node = AdjNode(src)
        node.next = self.graph[dest]
        self.graph[dest] = node

In this code, I'm not able to wrap my head around the add_edge method. I don't understand the lines that I've commented with "Please Explain". I know the comments in the code itself should suffice to understand the code but I'm sorry I couldn't understand. I researched on stack overflow, google, etc. There were answers available, but all were either too generic or not at all easy to understand. Experts, can you please help me understand what are those two lines of code doing? P.S - Sorry about the formatting and grammar. CodeLink

I'm currently trying to implement the shortest path algorithm, using a graph implemented through adjacency lists. If I understand correctly the idea of the algorithm, I should make the values of all elements in my array of adjacency lists equal some value representing infinity. In this toy example, I try to set the value of 9999 to the vertexes of the lists and fail for unknown to me reasons. It seems, that one of my elements loses a pointer to another, but I cannot understand why.

Even if I solved this problem, I still have one big issue: I don't understand how am I supposed to continue with the implementation of this algorithm afterwards. Am I supposed to replace the values of every vertex in the list with the value of the weight of the line connecting it to the head element of the list?

Consider: I have a list 0 |-> 1 -> 2, 1| -> 0 -> 3, 2| -> 0, 3| ->1. If I say these are my adjacency lists, how should I proceed? Should I replace the vertexes of my list with the value representing infinity, and then replace them with the sum of the weight and the value of the previous vertex? If so, can you help me understand how I shoud implement it, without mismanaging my pointers?

Code : https://pastebin.com/a3Uz5mub

For many students, the graph data structure can be intimidating and difficult to learn. In fact, some of their properties can be baffling to even experienced developers and computer science graduates who haven't worked with them for a while.

But graphs are interesting and integral, as they are a vital way of modeling and displaying information in the world around us. We can use graphs to do incredible things with computers. As an example, social networks are simply huge graphs at their core. Companies like LinkedIn and Google utilize many graph algorithms understand complex networks and relationships.

We at AlgoDaily have created a new free, visual, interactive guide to how to implement graphs. We ask that you take a look here and provide us feedback: https://algodaily.com/lessons/implementing-graphs-edge-list-adjacency-list-adjacency-matrix

Is there a way to get the polygon list from an adjacency matrix? For example, given an adjacency matrix T:

     v1  v2  v3  v4  v5  v6  v7  v8  v9  v10
v1        1   1      
v2    1              1 
v3    1           1
v4            1      1 
v5        1       1      1
v6                   1       1            1
v7                       1       1
v8                           1       1
v9                               1        1
v10                      1          1 

The polygon list is (Update: adjacency list)

f 1 2 4 5  3
f 6 7 9 10 8

https://gist.github.com/Jack-Tilley/203d5fa06af44201f6d064f74d39bdc2

This code takes an input url of any site and scrapes the site and all of its links in order to generate an adjacency matrix to display a directed network graph of what the site looks like.

Please let me know what you think!

So we are doing an Adjacency List graph for a class of mine and for the most part I'm getting it down except for one method my professor gave us for removal of a vertex. Vertex in this program is a private class with a <T> value and an arraylist of adjacencies

The code is:

public List<T> remove(T v){
     Vertex vertex = getVertex(v);   //gets the vertex at the value passed
        if(vertex == null)
               return null;
        verticies.remove(vertex);    //vertices an array list
        ArrayList<Vertex> adj= new ArrayList(v);
            for(Vertex av: Vertex.getAdjacences()){
                adj.add(av.getValue());
            }
            return adj;
   }

There's a bunch of errors with trying to make an ArrayList of vertexes with an ArrayList of objects and referencing the getAdjacencies method. I have no clue why he gave us this as it seems like it doesn't even work

Hi. Im working on a project and am rather indecisive about how to manage my data. The project basically checks if there's a path between two nodes in an oriented graph. Then it groups the nodes in subsections, and in each subsection you can reach any node of that subsection starting in any given node. The inputs are as large as 40k nodes and 90k edges. What do you recommend using? The memory used doesnt matter much, but the time it takes the algorithm to solve the problem matters a lot. Thanks!

Hello

I'm tryng to create basic implementation of graph using adjacency list. I created class graph with std::unordered_map as private member with typename T and std::list<T> as key-value pairs.
When I insert new edge, it first finds key and then pushes edge's destination value on list.

Please guide me if I'm doing it wrong.
Thanks.

Link: https://github.com/Lukas713/dataStruturesAndAlgorithms/blob/master/OOP/Graph/adjacentList.cpp

After struggling with finding information on getting started in GvGs, and flat out just being too lazy to click through all the territories I am left asking this question:

Is there a excel spreadsheet or tool somewhere with a list of all the territories, their primetimes, and attributes like attack-able from a siege camp?? If someone wants to help me assemble the data, I will happily create and host a web application / database with this data.

So, I'm currently trying to write code for my Graph(unweighted,directed) program and I'm having a little trouble understanding what/how to create an adjacency list. I saw I could create an List of ArrayLists (where the first dimension corresponds to the vertex and the inner nested list are the edges for the corresponding vertex)

List<List<String>> stringArray = new ArrayList<List<String>>();

stringArray.add(new ArrayList<String>());

stringArray.get(0).add("A new string");

I found this online. My question is, how would I add elements to just the first level? For example, if I had vertices a b c d e. And a is connected to b and d, and vertex d is connected to e,b, a.

I want to add to the first level, vertices a b c d e . Then I want to add vertices b and d to the nested list found in the first index of my ArrayList corresponding to the first vertex a, and then the nested list containing elements b and d. I've looked up nested lists and I'm super confused. I tried adding elements to the first layer but I'm just getting compile errors, adding to the second layer works.

TL;DR I need to add elements to the outer list in a lists of lists, and I want to add elements to the inner list.

Just started learning about graph and it's various representations (matrix and adjacency list). Now I found that the adjacency list representation can be implemented in various ways:

1. Array of arrays (where we have one index in main array for each vertices and adjacent vertices are in subarrays at each of this index)
2. Array of linked lists (most common implementation I have seen)
3. Map of array (same as array of arrays, except that outer array is now a Map)

Was wondering why would I prefer one of these implementation over the other. Is one implementation more common or efficient in any way or they all the same?