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// Exercise 1.5.7 (Solution published at http://algs4.cs.princeton.edu/)
package algs15;
import java.util.Arrays;
import stdlib.*;
/* **************************************************************************
 *  Compilation:  javac QuickUnionUF.java
 *  Execution:  java QuickUnionUF < input.txt
 *  Dependencies: StdIn.java StdOut.java
 *
 *  Quick-union algorithm.
 *
 *  % java QuickUnionUF < largeUF.txt
 *  QuickUnionUF # components: 6 [8332.928000] // More than 2 hours
 *
 ****************************************************************************/

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

  // instantiate N isolated components 0 through N-1
  public QuickUnionUF(int N) {
    id = new int[N];
    count = N;
    for (int i = 0; i < N; i++) {
      id[i] = i;
    }
  }

  // return number of connected components
  public int count() {
    return count;
  }

  // return root of component corresponding to element p
  public int find(int p) {
    while (p != id[p])
      p = id[p];
    return p;
  }

  // are elements p and q in the same component?
  public boolean connected(int p, int q) {
    return find(p) == find(q);
  }

  // merge components containing p and q
  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 static void main(String[] args) {
    StdIn.fromFile ("data/tinyUF.txt");
    //StdIn.fromFile ("data/mediumUF.txt");
    //StdIn.fromFile ("data/largeUF.txt");

    int N = StdIn.readInt();
    QuickUnionUF uf = new QuickUnionUF(N);

    // 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);
      StdOut.println(p + " " + q);
      GraphvizBuilder.ufToFile (uf.id);
    }
    StdOut.format("QuickUnionUF # components: %d [%f]\n", uf.count(), sw.elapsedTime ());
  }
}