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DisjoinSet.java
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DisjoinSet.java
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import java.util.HashMap;
import java.util.Map;
// A class to represent a disjoint set
class DisjointSet
{
private Map<Integer, Integer> parent = new HashMap<>();
// perform MakeSet operation
public void makeSet(int[] universe)
{
// create `n` disjoint sets (one for each item)
for (int i: universe) {
parent.put(i, i);
}
}
// Find the root of the set in which element `k` belongs
public int Find(int k)
{
// if `k` is root
if (parent.get(k) == k) {
return k;
}
// recur for the parent until we find the root
return Find(parent.get(k));
}
// Perform Union of two subsets
public void Union(int a, int b)
{
// find the root of the sets in which elements `x` and `y` belongs
int x = Find(a);
int y = Find(b);
parent.put(x, y);
}
}
class Main
{
public static void printSets(int[] universe, DisjointSet ds)
{
for (int i: universe) {
System.out.print(ds.Find(i) + " ");
}
System.out.println();
}
// Disjoint–Set data structure (Union–Find algorithm)
public static void main(String[] args)
{
// universe of items
int[] universe = { 1, 2, 3, 4, 5 };
// initialize `DisjointSet` class
DisjointSet ds = new DisjointSet();
// create a singleton set for each element of the universe
ds.makeSet(universe);
printSets(universe, ds);
ds.Union(4, 3); // 4 and 3 are in the same set
printSets(universe, ds);
ds.Union(2, 1); // 1 and 2 are in the same set
printSets(universe, ds);
ds.Union(1, 3); // 1, 2, 3, 4 are in the same set
printSets(universe, ds);
}
}