resolve #832 - Disjoint Set Union [Java]

Disjoint_union_set/DisjointUnionSet.java

@@ -0,0 +1,93 @@
+//Disjoint Set Data Structure
+public class DisjointUnionSet {
+    int[] rank, parent;
+    int size;
+
+    // Parameterized constructor
+    public DisjointUnionSet(int size) {
+        parent = new int[size];
+        rank = new int[size];
+        this.size = size;
+        init();
+    }
+
+    /**
+     * 
+     * @param val
+     * @return representative of set to which val belongs
+     */
+    public int find(int val) {
+        if (this.parent[val] == val) // if val is parent of itself then return val
+            return val;
+        // if val is not parent of itself Then
+        // val is not the representative of set to which it belongs
+        // hence recursively call find on val's parent
+        // while performing the path compression
+        return this.parent[val] = find(this.parent[val]);
+    }
+
+    /**
+     * Unites the set that includes val1 and set that includes val2
+     * 
+     * @param val1 element of first set
+     * @param val2 element of second set
+     */
+    public void union(int val1, int val2) {
+        // Find representatives of set to which val1 and val2 belongs
+        int val1Representative = find(val1);
+        int val2Representative = find(val2);
+
+        // Elements belong to same set, return
+        if (val1Representative == val2Representative)
+            return;
+
+        // if val1's representative rank is less than val2's representative
+        if (rank[val1Representative] < rank[val2Representative])
+            // Move val2 under val1 so depth of tree remains less
+            this.parent[val1Representative] = val2Representative;
+
+        // else if val1's representative rank is less than val2's representative
+        else if (this.rank[val2Representative] < this.rank[val1Representative])
+            // Move val1 under val2 so depth of tree remains less
+            this.parent[val2Representative] = val1Representative;
+
+        // if the ranks are same
+        else {
+            // move val1 under val2
+            parent[val2Representative] = val1Representative;
+            // increment resultant tree rank by 1
+            rank[val1Representative] += 1;
+
+        }
+
+    }
+
+    /**
+     * initializes the parent array
+     */
+    private void init() {
+        for (int i = 0; i < this.size; i++) {
+            parent[i] = i; // initially all the elements are in their own set
+        }
+    }
+
+}
+
+// Driver code
+class Main {
+    public static void main(String[] args) {
+        // create a dsu for 5 elements
+        DisjointUnionSet dsu = new DisjointUnionSet(5);
+
+        System.out.println("Representative of 1 is :" + dsu.find(1)); // get representative of 1
+        System.out.println("Representative of 2 is :" + dsu.find(2)); // get representative of 2
+
+
+        System.out.println("\nApplying union on set to which 1 and 2 belong\n");
+        dsu.union(1, 2); // do union of of set to which 1 and 2 belongs
+
+        System.out.println("Representative of 1 is :" + dsu.find(1)); // get representative of 1
+        System.out.println("Representative of 2 is :" + dsu.find(2)); // get representative of 2
+
+    }
+}