2022 May 30
  • What is called the number associated with a graph’s edge? The edge’s weight.

  • What is the difference between a weighted and an unweighted graph? A weighted graph has weight (a number) on its' edges. That number means a distance or a cost related to moving between the nodes. An unweighted graph does not have weight on its' edges.

  • Regarding graph algorithms, how to choose between Bread-first search and Dijkstra algorithms? To find the path with the fewest nodes on an unweighted graph, you use Bread-first search. To find the shortest path on a weighted graph you use Dijkstra.

  • Which are the 4 steps for the Dijkstra’s algorithm? . Find the node with the lesser weight . Update the costs of the neighbor of this node . Repeat until done for each node in the graph . Calculate the final path.

  • What is a cycle on a graph? It is e.g. when you have a node A, travel to others and come back to node A.

  • How to get the shortest path on a weighted graph that has cycles? That is not possible.

  • What is an undirected graph? It is a graph with no direction between 2 nodes, which means they point to each other.

  • Which are the 2 conditions where Dijkstra’s algorithm cannot be applied? . Graphs with cycles . Graphs with negative weight

  • How do you implement the Dijkstra’s algorithm? You can have a table with the name and cost of each node, and a column with the parent of each node. The last value on the “cost” column is always updated. E.g.:

Parent 		| Node 		| Cost
A		| B		| 5
B		| C		| 0
C		| D		| 30 35
  • Besides being applied to calculate distances, where can Dijkstra’s algorithm can also be applied? When you need to minimize something. E.g., minimize the amount of money spent to buy different products given a limited amount of money.

  • What effect does graphs with negative weight edges have on the Dijkstra’s algorithm? They break it. To find the shortest path when you have negative-weighted edges you can use e.g. the Bellman-Ford algorithm.

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