《算法》第四章部分程序 part 1

▶ 书中第四章部分程序，加上自己补充的代码，包含无向 / 有向图类

● 无向图类

 package package01;

 import java.util.NoSuchElementException;
 import edu.princeton.cs.algs4.In;
 import edu.princeton.cs.algs4.StdOut;
 import edu.princeton.cs.algs4.Bag;
 import edu.princeton.cs.algs4.Stack;

 public class class01
 {
     private static final String NEWLINE = System.getProperty("line.separator");

     private final int V;
     private int E;
     private Bag<Integer>[] adj;

     public class01(int inputV)
     {
         if (inputV < 0)
             throw new IllegalArgumentException("\n<Constructor> V < 0.\n>");
         V = inputV;
         E = 0;
         adj = (Bag<Integer>[]) new Bag[V];
         for (int v = 0; v < V; v++)
             adj[v] = new Bag<Integer>();
     }

     public class01(In in)
     {
         try
         {
             V = in.readInt();
             if (V < 0)
                 throw new IllegalArgumentException("\n<Constructor> V < 0.\n>");
             adj = (Bag<Integer>[]) new Bag[V];
             for (int v = 0; v < V; v++)
                 adj[v] = new Bag<Integer>();
             int E = in.readInt();
             if (E < 0)
                 throw new IllegalArgumentException("\n<Constructor> E < 0.\n>");
             for (int i = 0; i < E; i++)
             {
                 int v = in.readInt();
                 int w = in.readInt();
                 //validateVertex(v);
                 //validateVertex(w);
                 addEdge(v, w);
             }
         }
         catch (NoSuchElementException e)
         {
             throw new IllegalArgumentException("\n<Constructor> parameter error.\n");
         }
     }

     public class01(class01 G)
     {
         this(G.V());                    // "this" 等价于 class01，即构造函数
         E = G.E();
         for (int v = 0; v < G.V(); v++) // 使用栈来遍历原图邻接表，遍历栈时建立新图的邻接表
         {
             Stack<Integer> edgeStack = new Stack<Integer>();
             for (int w : G.adj[v])
                 edgeStack.push(w);
             for (int w : edgeStack)
                 adj[v].add(w);
         }
     }

     public int V()
     {
         return V;
     }

     public int E()
     {
         return E;
     }

     public void addEdge(int v, int w)
     {
         //validateVertex(v);
         //validateVertex(w);
         adj[v].add(w);
         adj[w].add(v);
         E++;
     }

     public Iterable<Integer> adj(int v) // 生成迭代器
     {
         //validateVertex(v);
         return adj[v];
     }

     public int degree(int v)            // 计算顶点的度数
     {
         //validateVertex(v);
         return adj[v].size();
     }

     public String toString()            // toString 接口
     {
         StringBuilder s = new StringBuilder();
         s.append(V + " vertices, " + E + " edges " + NEWLINE);
         for (int v = 0; v < V; v++)
         {
             s.append(v + ": ");
             for (int w : adj[v])
                 s.append(w + " ");
             s.append(NEWLINE);
         }
         return s.toString();
     }

     /*
     private void validateVertex(int v)
     {
         if (v < 0 || v >= V)
         throw new IllegalArgumentException("\n<validateVertex> v < 0 || v >= V.\n>");
     }
     */

     public static void main(String[] args)
     {
         In in = new In(args[0]);        // 输入第一行为顶点数，第二行为边数，以后每行为一条边的两个顶点
         class01 G = new class01(in);
         StdOut.println(G);
     }
 }

● 有向图类，只注释了与无向图不同的地方

 package package01;

 import java.util.NoSuchElementException;
 import edu.princeton.cs.algs4.In;
 import edu.princeton.cs.algs4.StdOut;
 import edu.princeton.cs.algs4.Bag;
 import edu.princeton.cs.algs4.Stack;

 public class class01
 {
     private static final String NEWLINE = System.getProperty("line.separator");

     private final int V;
     private int E;
     private Bag<Integer>[] adj;
     private int[] indegree;         // 每个顶点的入度

     public class01(int inputV)
     {
         if (inputV < 0)
             throw new IllegalArgumentException("\n<Constructor> V < 0.\n>");
         V = inputV;
         E = 0;
         adj = (Bag<Integer>[]) new Bag[V];
         for (int v = 0; v < V; v++)
             adj[v] = new Bag<Integer>();
         indegree = new int[V];      // 初始化入度
     }

     public class01(In in)
     {
         try
         {
             V = in.readInt();
             if (V < 0)
                 throw new IllegalArgumentException("\n<Constructor> V < 0.\n>");
             adj = (Bag<Integer>[]) new Bag[V];
             for (int v = 0; v < V; v++)
                 adj[v] = new Bag<Integer>();
             int E = in.readInt();
             if (E < 0)
                 throw new IllegalArgumentException("\n<Constructor> E < 0.\n>");
             for (int i = 0; i < E; i++)
             {
                 int v = in.readInt();
                 int w = in.readInt();
                 addEdge(v, w);
             }
             indegree = new int[V];  // 初始化入度
         }
         catch (NoSuchElementException e)
         {
             throw new IllegalArgumentException("\n<Constructor> parameter error.\n");
         }
     }

     public class01(class01 G)
     {
         this(G.V());
         E = G.E();
         for (int v = 0; v < G.V(); v++)
         {
             Stack<Integer> edgeStack = new Stack<Integer>();
             for (int w : G.adj[v])
                 edgeStack.push(w);
             for (int w : edgeStack)
                 adj[v].add(w);
         }
         for (int v = 0; v < V; v++)         // 拷贝所有顶点的入度
             indegree[v] = G.indegree(v);
     }

     public int V()
     {
         return V;
     }

     public int E()
     {
         return E;
     }

     public void addEdge(int v, int w)
     {
         //validateVertex(v);
         //validateVertex(w);
         adj[v].add(w);
         indegree[w]++;                      // 添加变的时候只添加一次，并更新重点的入度
         E++;
     }

     public Iterable<Integer> adj(int v)
     {
         //validateVertex(v);
         return adj[v];
     }

     public int outdegree(int v)             // 顶点的出度
     {
         //validateVertex(v);
         return adj[v].size();
     }

     public int indegree(int v)              // 顶点的入度
     {
         //validateVertex(v);
         return indegree[v];
     }

     public class01 reverse()                // 反向图
     {
         class01 reverse = new class01(V);   // 把复制构造函数改成不用栈即可
         for (int v = 0; v < V; v++)
         {
             for (int w : adj(v))
                 reverse.addEdge(w, v);
         }
         return reverse;
     }

     public String toString()
     {
         StringBuilder s = new StringBuilder();
         s.append(V + " vertices, " + E + " edges " + NEWLINE);
         for (int v = 0; v < V; v++)
         {
             s.append(v + ": ");
             for (int w : adj[v])
                 s.append(w + " ");
             s.append(NEWLINE);
         }
         return s.toString();
     }

     /*
     private void validateVertex(int v)
     {
         if (v < 0 || v >= V)
             throw new IllegalArgumentException("\n<validateVertex> v < 0 || v >= V.\n>");
     }
     */

     public static void main(String[] args)
     {
         In in = new In(args[0]);            // 输入第一行为顶点数，第二行为边数，以后每行依次为一条边的起点和终点
         class01 G = new class01(in);
         StdOut.println(G);
     }
 }