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package algs15;
import java.util.Arrays;
import stdlib.*;
/* **************************************************************************
 *  Compilation:  javac WeightedQuickUnionHalvingUF.java
 *  Execution:  java WeightedQuickUnionHalvingUF < input.txt
 *  Dependencies: StdIn.java StdOut.java
 *
 *  Weighted quick-union with path compression via halving.
 *
 ****************************************************************************/

public class XWeightedHalvingUF implements UF {
  private int[] id;    // id[i] = parent of i
  private int[] sz;    // sz[i] = number of objects in subtree rooted at i
  private int count;   // number of components

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

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

  // return component identifier for component containing p
  public int find(int p) {
    while (p != id[p]) {
      id[p] = id[id[p]];    // path compression by halving
      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, making smaller root point to larger one
  public void union(int p, int q) {
    int pid = find(p);
    int qid = find(q);
    if (pid == qid) return;
    // in the case of a tie, p is the champion
    if   (sz[pid] < sz[qid]) { id[pid] = qid; sz[qid] += sz[pid]; }
    else                     { id[qid] = pid; sz[pid] += sz[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();
    XWeightedHalvingUF uf = new XWeightedHalvingUF(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("XWeightedQuickUnionHalvingUF # components: %d [%f]", uf.count(), sw.elapsedTime ());
  }

}