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>());
        Topological topological2 = new Topological("C2", 1, new ArrayList<Topological>());
        Topological topological3 = new Topological("C3", 2, new ArrayList<Topological>());
        Topological topological4 = new Topological("C4", 1, new ArrayList<Topological>());
        Topological topological5 = new Topological("C5", 2, new ArrayList<Topological>());
        Topological topological6 = new Topological("C6", 1, new ArrayList<Topological>());
        Topological topological7 = new Topological("C7", 2, new ArrayList<Topological>());
        Topological topological8 = new Topological("C8", 2, new ArrayList<Topological>());
        Topological topological9 = new Topological("C9", 0, new ArrayList<Topological>());
        Topological topological10 = new Topological("C10", 1, new ArrayList<Topological>());
        Topological topological11 = new Topological("C11", 1, new ArrayList<Topological>());
        Topological topological12 = new Topological("C12", 3, new ArrayList<Topological>());

        //将节点添加后驱
        List<Topological> 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<Topological> topologicals = new ArrayList<Topological>();
        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<Topological> topologicalListForReturn = new ArrayList<Topological>();
        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。