[Function add]

1.Add the function of the topological graph.

Author: Seanforfun

Algorithm(4th_Edition)/src/ca/mcmaster/chapter/four/graph/directed/Topological.java

@@ -0,0 +1,31 @@
+package ca.mcmaster.chapter.four.graph.directed;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+
+public class Topological {
+	private Iterable<Integer> order;
+	public Topological(Digraph g){
+		DirectedCycle dc = new DirectedCycle(g);
+		if(!dc.hasCycle()){
+			DepthFirstOrder dfo = new DepthFirstOrder(g);
+			order = dfo.reversePost();
+		}
+	}
+	public Iterable<Integer> order(){
+		return order;
+	}
+	public boolean isDAG(){
+		return order != null;
+	}
+	public static void main(String[] args) throws FileNotFoundException {
+		Digraph g = new DigraphImpl(new FileInputStream(new File("src/ca/mcmaster/chapter/four/graph/tinyDG.txt")));
+		Topological topological  = new Topological(g);
+		StringBuilder sb = new StringBuilder();
+		for(int i : topological.order()){
+			sb.append(i + " ");
+		}
+		System.out.println(sb.toString());
+	}
+}

DataStructrue/Graph/DirectedGraph.md

@@ -388,3 +388,25 @@ public class DepthFirstOrder {
 	}
 }
 ```
+
+### 拓扑排序
+>给定一张有向图，将所有的顶点排序，使得所有的有向边均从排在前面的元素指向排在后面的元素。
+>有环图画不出拓扑图，因为有环图无法确定环上定点的顺序。
+```Java
+public class Topological {
+	private Iterable<Integer> order;
+	public Topological(Digraph g){
+		DirectedCycle dc = new DirectedCycle(g);
+		if(!dc.hasCycle()){
+			DepthFirstOrder dfo = new DepthFirstOrder(g);
+			order = dfo.reversePost();	//depth first order的逆后序就是拓扑图的顺序。
+		}
+	}
+	public Iterable<Integer> order(){
+		return order;
+	}
+	public boolean isDAG(){
+		return order != null;
+	}
+}
+```

DataStructrue/Graph/Topological.java

@@ -0,0 +1,31 @@
+package ca.mcmaster.chapter.four.graph.directed;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+
+public class Topological {
+	private Iterable<Integer> order;
+	public Topological(Digraph g){
+		DirectedCycle dc = new DirectedCycle(g);
+		if(!dc.hasCycle()){
+			DepthFirstOrder dfo = new DepthFirstOrder(g);
+			order = dfo.reversePost();
+		}
+	}
+	public Iterable<Integer> order(){
+		return order;
+	}
+	public boolean isDAG(){
+		return order != null;
+	}
+	public static void main(String[] args) throws FileNotFoundException {
+		Digraph g = new DigraphImpl(new FileInputStream(new File("src/ca/mcmaster/chapter/four/graph/tinyDG.txt")));
+		Topological topological  = new Topological(g);
+		StringBuilder sb = new StringBuilder();
+		for(int i : topological.order()){
+			sb.append(i + " ");
+		}
+		System.out.println(sb.toString());
+	}
+}