01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
 
package algs15;
import java.util.Arrays;
import  stdlib.*;

/* **************************************************************************
 *  Compilation:  javac QuickUnionPathCompressionUF.java
 *  Execution:  java QuickUnionPathCompressionUF < input.txt
 *  Dependencies: StdIn.java StdOut.java
 *
 *  Quick-union with path compression.
 *
 ****************************************************************************/

public class CompressionUF implements UF {
  private int[] id;    // id[i] = parent of i
  private int count;   // number of components

  // Create an empty union find data structure with N isolated sets.
  public CompressionUF(int N) {
    count = N;
    id = new int[N];
    for (int i = 0; i < N; i++) {
      id[i] = i;
    }
  }

  // Return the number of disjoint sets.
  public int count() {
    return count;
  }
  
  // Are objects p and q in the same set?
  public boolean connected(int p, int q) {
    return find(p) == find(q);
  }
  
  // Return component identifier for component containing p
  public int find(int p) {
    int root = p;
    while (root != id[root])
      root = id[root];
    while (id[p] != root) {
      int newp = id[p];
      id[p] = root;
      if (TestUF.SHOW_COMPRESSION_STEPS) { StdOut.format("%2d %2d> %2d%s\n", p, root, this.count(), this); toGraphviz(); }
      p = newp;
    }
    return root;
  }

  // Replace sets containing p and q with their union.
  public void union(int p, int q) {
    int pid = find(p); // loser
    int qid = find(q); // champion
    if (pid == qid) return;
    id[pid] = qid;
    count--;
  }

  public String toString() { return Arrays.toString (id); }
  public void toGraphviz() { GraphvizBuilder.ufToFile (id); }

  public static void main(String[] args) {
    boolean print = true;
    StdIn.fromFile ("data/tinyUF.txt"); 
    //StdIn.fromFile ("data/mediumUF.txt"); print = false;
    //StdIn.fromFile ("data/largeUF.txt"); print = false;

    int N = StdIn.readInt();
    CompressionUF uf = new CompressionUF(N);
    if (print) { uf.toGraphviz(); StdOut.println("   : " + uf); }

    // read in a sequence of pairs of integers (each in the range 0 to N-1),
    // calling find() for each pair: If the members of the pair are not already
    // call union() and print the pair.
    Stopwatch sw = new Stopwatch ();
    while (!StdIn.isEmpty()) {
      int p = StdIn.readInt();
      int q = StdIn.readInt();
      if (uf.connected(p, q)) continue;
      uf.union(p, q);
      if (print) { StdOut.println(p + " " + q + ": " + uf); uf.toGraphviz(); }
    }
    StdOut.format("CompressionUF # components: %d [%f]\n", uf.count(), sw.elapsedTime ());
  }

}