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Enhance docs, add more tests in JohnsonsAlgorithm (#5964)

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This commit is contained in:
Hardik Pawar
2024-10-24 10:48:12 +05:30
committed by GitHub
parent be0b1d58d6
commit 1b51e3e988
2 changed files with 59 additions and 56 deletions
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15
src/main/java/com/thealgorithms/datastructures/graphs/JohnsonsAlgorithm.java
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@ -21,17 +21,18 @@ import java.util.List;
*/
public final class JohnsonsAlgorithm {
// Constant representing infinity
private static final double INF = Double.POSITIVE_INFINITY;
/**
* A private constructor to hide the implicit public one.
*/
private JohnsonsAlgorithm() {
}
/**
* Executes Johnson's algorithm on the given graph.
* Steps:
* 1. Add a new vertex to the graph and run Bellman-Ford to compute modified weights
* 2. t the graph using the modified weights
* 3. Run Dijkstra's algorithm for each vertex to compute the shortest paths
* The final result is a 2D array of shortest distances between all pairs of vertices.
*
* @param graph The input graph represented as an adjacency matrix.
* @return A 2D array representing the shortest distances between all pairs of vertices.
@ -40,13 +41,10 @@ public final class JohnsonsAlgorithm {
int numVertices = graph.length;
double[][] edges = convertToEdgeList(graph);
// Step 1: Add a new vertex and run Bellman-Ford
double[] modifiedWeights = bellmanFord(edges, numVertices);
// Step 2: Reweight the graph
double[][] reweightedGraph = reweightGraph(graph, modifiedWeights);
// Step 3: Run Dijkstra's algorithm for each vertex
double[][] shortestDistances = new double[numVertices][numVertices];
for (int source = 0; source < numVertices; source++) {
shortestDistances[source] = dijkstra(reweightedGraph, source, modifiedWeights);
@ -74,7 +72,6 @@ public final class JohnsonsAlgorithm {
}
}
// Convert the List to a 2D array
return edgeList.toArray(new double[0][]);
}
@ -89,7 +86,7 @@ public final class JohnsonsAlgorithm {
private static double[] bellmanFord(double[][] edges, int numVertices) {
double[] dist = new double[numVertices + 1];
Arrays.fill(dist, INF);
dist[numVertices] = 0; // Distance to the new source vertex is 0
dist[numVertices] = 0;
// Add edges from the new vertex to all original vertices
double[][] allEdges = Arrays.copyOf(edges, edges.length + numVertices);