/* Soot - a J*va Optimization Framework
* Copyright (C) 2007 Manu Sridharan
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
package soot.jimple.spark.ondemand.genericutil;
import java.util.Arrays;
public final class DisjointSets {
private int[] array;
/**
* Construct a disjoint sets object.
*
* @param numElements
* the initial number of elements--also the initial number of
* disjoint sets, since every element is initially in its own
* set.
*/
public DisjointSets(int numElements) {
array = new int[numElements];
Arrays.fill(array, -1);
}
/**
* union() unites two disjoint sets into a single set. A union-by-size
* heuristic is used to choose the new root. This method will corrupt the
* data structure if root1 and root2 are not roots of their respective sets,
* or if they're identical.
*
* @param root1
* the root of the first set.
* @param root2
* the root of the other set.
*/
public void union(int root1, int root2) {
assert array[root1] < 0;
assert array[root2] < 0;
assert root1 != root2;
if (array[root2] < array[root1]) { // root2 has larger tree
array[root2] += array[root1]; // update # of items in root2's tree
array[root1] = root2; // make root2 new root
} else { // root1 has equal or larger tree
array[root1] += array[root2]; // update # of items in root1's tree
array[root2] = root1; // make root1 new root
}
}
/**
* find() finds the (int) name of the set containing a given element.
* Performs path compression along the way.
*
* @param x
* the element sought.
* @return the set containing x.
*/
public int find(int x) {
if (array[x] < 0) {
return x; // x is the root of the tree; return it
} else {
// Find out who the root is; compress path by making the root x's
// parent.
array[x] = find(array[x]);
return array[x]; // Return the root
}
}
}