算法第四版用eclipse实现书中UnionFind例子

一安装环境

下载完成后C:\Users\zle 下面会有algs4 文件夹

原文：

Our installer downloads, installs, and configures the Java programming environment you will be using, including Java SE 7, DrJava, the textbook libraries, and the Command Prompt.

Log in to the user account in which you will be programming. Your account must have Administrator privileges and you must be connected to the Internet.
Download algs4.exe and double-click it to perform the installation. If you receive a User Account Control alert before the installation, click Yes or Allow; if you receive a Program Compatibility Assistant alert after the installation, click This program installed correctly.
If the installation succeeds, you will see the following:
- A Command Prompt windows containing approximately this execution log
- A Standard Drawing window containing a blue bullseye and textbook graphic.
Note that the installation can take several minutes or longer if you have a slow internet connection.
Delete algs4.exe.

二将这个文件夹复制到eclipse工作环境下

3 在eclipse中设置cmd环境

选择 External tools configrations

Name 名字随便取我的是UF1.5

Location 是cmd的目录

working director 默认的工作目录

三编写程序并运行

 1 import edu.princeton.cs.algs4.StdIn;
 2 import edu.princeton.cs.algs4.StdOut;
 3 
 4 public class WeightedQuickUnionUF {
 5     private int[] id;    // id[i] = parent of i
 6     private int[] sz;    // sz[i] = number of objects in subtree rooted at i
 7     private int count;   // number of components
 8 
 9     // Create an empty union find data structure with N isolated sets.
10     public WeightedQuickUnionUF(int N) {
11         count = N;
12         id = new int[N];
13         sz = new int[N];
14         for (int i = 0; i < N; i++) {
15             id[i] = i;
16             sz[i] = 1;
17         }
18     }
19 
20     // Return the number of disjoint sets.
21     public int count() {
22         return count;
23     }
24 
25     // Return component identifier for component containing p
26     public int find(int p) {
27         while (p != id[p])
28             p = id[p];
29         return p;
30     }
31 
32    // Are objects p and q in the same set?
33     public boolean connected(int p, int q) {
34         return find(p) == find(q);
35     }
36 
37   
38    // Replace sets containing p and q with their union.
39     public void union(int p, int q) {
40         int i = find(p);
41         int j = find(q);
42         if (i == j) return;
43 
44         // make smaller root point to larger one
45         if   (sz[i] < sz[j]) { id[i] = j; sz[j] += sz[i]; }
46         else                 { id[j] = i; sz[i] += sz[j]; }
47         count--;
48     }
49 
50 
51     public static void main(String[] args) {
52         int N = StdIn.readInt();
53         WeightedQuickUnionUF uf = new WeightedQuickUnionUF(N);
54 
55         // read in a sequence of pairs of integers (each in the range 0 to N-1),
56          // calling find() for each pair: If the members of the pair are not already
57         // call union() and print the pair.
58         while (!StdIn.isEmpty()) {
59             int p = StdIn.readInt();
60             int q = StdIn.readInt();
61             if (uf.connected(p, q)) continue;
62             uf.union(p, q);
63             StdOut.println(p + " " + q);
64         }
65         StdOut.println("# components: " + uf.count());
66     }
67 
68 }