《算法》第二章部分程序 part 5

▶ 书中第二章部分程序，加上自己补充的代码，包括利用优先队列进行多路归并和堆排序

● 利用优先队列进行多路归并

 package package01;

 import edu.princeton.cs.algs4.IndexMinPQ;
 import edu.princeton.cs.algs4.In;
 import edu.princeton.cs.algs4.StdOut;

 public class class01
 {
     private class01() {}

     private static void merge(In[] streams)
     {
         int n = streams.length;
         IndexMinPQ<String> pq = new IndexMinPQ<String>(n);
         for (int i = 0; i < n; i++)                     // 初始化队列，每个流输入一个元素
         {
             if (!streams[i].isEmpty())
                 pq.insert(i, streams[i].readString());
         }
         for (;!pq.isEmpty();)
         {
             StdOut.print(pq.minKey() + " ");            // 每当输出来自某个流的元素，就从该流插入一个元素
             int i = pq.delMin();
             if (!streams[i].isEmpty())
                 pq.insert(i, streams[i].readString());
         }
         StdOut.println();
     }

     public static void main(String[] args)
     {
         int n = args.length;
         In[] streams = new In[n];                       // 初始化输入流，输入多个文件
         for (int i = 0; i < n; i++)
             streams[i] = new In(args[i]);
         merge(streams);
     }
 }

● 堆排序

 package package01;

 import edu.princeton.cs.algs4.StdIn;
 import edu.princeton.cs.algs4.StdOut;

 public class class01
 {
     private class01() {}

     public static void sort(Comparable[] pq)
     {
         int n = pq.length;
         for (int k = n / 2; k >= 1; k--)  // 建堆
             sink(pq, k, n);
         for (; n > 1;)                    // 每次将最大元素交换到最后，重新调整前面的部分
         {
             exch(pq, 1, n--);
             sink(pq, 1, n);
         }
     }

     private static void sink(Comparable[] pq, int k, int n)
     {
         for (int j = k << 1; j <= n; exch(pq, k, j), k = j, j = k << 1)
         {
             if (j < n && less(pq, j, j + 1))
                 j++;
             if (!less(pq, k, j))
                 break;
         }
     }

     private static boolean less(Comparable[] pq, int i, int j)
     {
         return pq[i - 1].compareTo(pq[j - 1]) < 0;
     }

     private static void exch(Object[] pq, int i, int j)
     {
         Object swap = pq[i - 1];
         pq[i - 1] = pq[j - 1];
         pq[j - 1] = swap;
     }

     private static void show(Comparable[] a)
     {
         for (int i = 0; i < a.length; i++)
             StdOut.println(a[i]);
     }

     public static void main(String[] args)
     {
         String[] a = StdIn.readAllStrings();
         class01.sort(a);
         show(a);
     }
 }