Create TopologicalSort.java

Author: joydeep1982

TopologicalSort.java

@@ -0,0 +1,89 @@
+package ds.algo.solution;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.Stack;
+
+public class TopologicalSort {
+
+	public static void main(String[] args) {
+		TopoNode a = new TopoNode("a");
+		TopoNode b = new TopoNode("b");
+		TopoNode c = new TopoNode("c");
+		TopoNode d = new TopoNode("d");
+		TopoNode e = new TopoNode("e");
+		TopoNode f = new TopoNode("f");
+		TopoNode g = new TopoNode("g");
+		TopoNode h = new TopoNode("h");
+		
+		a.addChild(c);
+		b.addChild(c).addChild(d);
+		c.addChild(e);
+		d.addChild(f);
+		e.addChild(f).addChild(h);
+		f.addChild(g);
+		
+		Set<TopoNode> nodes = new HashSet<>();
+		nodes.add(a);
+		nodes.add(b);
+		nodes.add(c);
+		nodes.add(d);
+		nodes.add(e);
+		nodes.add(f);
+		nodes.add(g);
+		
+		Stack<TopoNode> stack = new TopologicalSort().topoSort(nodes);
+		while(!stack.isEmpty()) {
+			System.out.println(stack.pop());
+		}
+	}
+	
+	private Stack<TopoNode> topoSort(Set<TopoNode> nodes) {
+		Stack<TopoNode> topoStack = new Stack<>();
+		Set<TopoNode> visited = new HashSet<>();
+		Set<TopoNode> allNodes = new HashSet<>(nodes);
+		
+		for (TopoNode topoNode : allNodes) {
+			sort(topoNode, topoStack, visited);
+		}
+		
+		return topoStack;
+	}
+	
+	private void sort(TopoNode node, Stack<TopoNode> topoStack, Set<TopoNode> visited) {
+		if (visited.contains(node)) {
+			return;
+		}
+		visited.add(node);
+		for (TopoNode childNode : node.getChildren()) {
+			sort(childNode, topoStack, visited);
+		}
+		topoStack.add(node);
+	}
+}
+
+class TopoNode {
+	
+	String value;
+	
+	Set<TopoNode> children;
+	
+	TopoNode(String val) {
+		this.children = new HashSet<TopoNode>();
+		this.value = val;
+	}
+	
+	public TopoNode addChild(TopoNode n) {
+		children.add(n);
+		return this;
+	}
+	
+	public Set<TopoNode> getChildren(){
+		return children;
+	}
+	
+	@Override
+	public String toString() {
+		return this.value;
+	}
+}