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TopologicalSorting.java
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TopologicalSorting.java
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package Graph;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class TopologicalSorting {
// Helper Edge class to describe edges in the graph
static class Edge {
int from, to, weight;
public Edge(int f, int t, int w) {
from = f;
to = t;
weight = w;
}
}
private static int dfs(int orderingIdx, int startNode, boolean[] visited,
int[] ordering, Map<Integer, List<Edge>> graph) {
visited[startNode] = true;
List<Edge> edges = graph.get(startNode);
if (edges != null)
for (Edge edge : edges)
if (!visited[edge.to])
orderingIdx = dfs(orderingIdx, edge.to, visited, ordering, graph);
ordering[orderingIdx] = startNode;
return orderingIdx - 1;
}
public static int[] topologicalSort(Map<Integer, List<Edge>> graph, int numNodes) {
int[] ordering = new int[numNodes];
boolean[] visited = new boolean[numNodes];
int orderingIdx = numNodes - 1; // since DFS, so we start adding the nodes from the leaf
for (int i = 0; i < numNodes; i++)
if (!visited[i])
orderingIdx = dfs(orderingIdx, i, visited, ordering, graph);
return ordering;
}
public static void main(String[] args) {
// Graph setup
final int N = 7;
Map<Integer, List<Edge>> graph = new HashMap<>();
for (int i = 0; i < N; i++)
graph.put(i, new ArrayList<>());
graph.get(0).add(new Edge(0, 1, 3));
graph.get(0).add(new Edge(0, 2, 2));
graph.get(0).add(new Edge(0, 5, 3));
graph.get(1).add(new Edge(1, 3, 1));
graph.get(1).add(new Edge(1, 2, 6));
graph.get(2).add(new Edge(2, 3, 1));
graph.get(2).add(new Edge(2, 4, 10));
graph.get(3).add(new Edge(3, 4, 5));
graph.get(5).add(new Edge(5, 4, 7));
int[] ordering = topologicalSort(graph, N);
// // Prints: [6, 0, 5, 1, 2, 3, 4]
System.out.println(java.util.Arrays.toString(ordering));
}
}