java拓扑_拓扑排序 java

import java.util.*;

/**

* 拓扑排序：(1)在有向图中选一个没有前驱的顶点且输出之 (2)从图中删除该顶点和所有以它为尾的弧

* 重复以上两步骤，直至全部顶点均已输出，或者当前图中不存在无前驱的顶点为止。后者说明有向图中有环。

**/

public class TopologicalTest {

private static final int V_COUNT = 12;

public static void main(String[] args) {

//初始化节点

Topological topological1 = new Topological("C1", 0, new ArrayList());

Topological topological2 = new Topological("C2", 1, new ArrayList());

Topological topological3 = new Topological("C3", 2, new ArrayList());

Topological topological4 = new Topological("C4", 1, new ArrayList());

Topological topological5 = new Topological("C5", 2, new ArrayList());

Topological topological6 = new Topological("C6", 1, new ArrayList());

Topological topological7 = new Topological("C7", 2, new ArrayList());

Topological topological8 = new Topological("C8", 2, new ArrayList());

Topological topological9 = new Topological("C9", 0, new ArrayList());

Topological topological10 = new Topological("C10", 1, new ArrayList());

Topological topological11 = new Topological("C11", 1, new ArrayList());

Topological topological12 = new Topological("C12", 3, new ArrayList());

//将节点添加后驱

List list = topological1.getTopologicals();

list.add(topological2);

list.add(topological4);

list.add(topological12);

list.add(topological3);

topological1.setTopologicals(list);

list = topological2.getTopologicals();

list.add(topological3);

topological2.setTopologicals(list);

list = topological3.getTopologicals();

list.add(topological5);

list.add(topological7);

list.add(topological8);

topological3.setTopologicals(list);

list = topological4.getTopologicals();

list.add(topological5);

topological4.setTopologicals(list);

list = topological5.getTopologicals();

list.add(topological7);

topological5.setTopologicals(list);

list = topological6.getTopologicals();

list.add(topological8);

topological6.setTopologicals(list);

list = topological9.getTopologicals();

list.add(topological10);

list.add(topological11);

list.add(topological12);

topological9.setTopologicals(list);

list = topological10.getTopologicals();

list.add(topological12);

topological10.setTopologicals(list);

list = topological11.getTopologicals();

list.add(topological6);

topological11.setTopologicals(list);

//将图中的节点放入列表

List topologicals = new ArrayList();

topologicals.add(topological1);

topologicals.add(topological2);

topologicals.add(topological3);

topologicals.add(topological4);

topologicals.add(topological5);

topologicals.add(topological6);

topologicals.add(topological7);

topologicals.add(topological8);

topologicals.add(topological9);

topologicals.add(topological10);

topologicals.add(topological11);

topologicals.add(topological12);

//定义一个列表来存放入度为零的节点

List topologicalListForReturn = new ArrayList();

int i = 0;

while(i++ <= V_COUNT) {

for(Topological each : topologicals) {

//判断一下是否已经在入度为0的列表中

//如果是，则返回，判断下一个

if(topologicalListForReturn.contains(each)) {

continue;

}

if(each.getIndegree() == 0) {

for(Topological topological : each.getTopologicals()) {

topological.setIndegree(topological.getIndegree() - 1);

}

topologicalListForReturn.add(each);

break;

}

}

}

//如果入度为0的节点数少于图总节点数，则存在环

if(topologicalListForReturn.size() < topologicals.size()) {

System.out.println("此图存在环");

}else {

for(Topological each : topologicalListForReturn) {

System.out.print(each.getName() + " ");

}

}

}

}

总结：入度为0的顶点即为没有前驱的顶点，删除顶点及以它为尾的弧的操作，则可换成以弧头顶点的入度减1来实现。