add: MergingCommunities

Author: Jer3myYu

java/Graphs/MergingCommunities.java

@@ -0,0 +1,60 @@
+import java.util.Arrays;
+
+public class UnionFind {
+    int[] parent;
+    int[] size;
+
+    public UnionFind(int size) {
+        this.parent = new int[size];
+        this.size = new int[size];
+        for (int i = 0; i < size; i++) {
+            this.parent[i] = i;
+        }
+        Arrays.fill(this.size, 1);
+    }
+
+    public void union(int x, int y) {
+        int repX = find(x);
+        int repY = find(y);
+        // If 'repX' represents a larger community, connect
+        // 'repY 's community to it.
+        if (this.size[repX] > this.size[repY]) {
+            this.parent[repY] = repX;
+            this.size[repX] += this.size[repY];
+        }
+        // Otherwise, connect 'rep_x's community to 'rep_y'.
+        else {
+            this.parent[repX] = repY;
+            this.size[repY] += this.size[repX];
+        }
+    }
+
+    public int find(int x) {
+        if (x == this.parent[x]) {
+            return x;
+        }
+        // Path compression.
+        this.parent[x] = find(this.parent[x]);
+        return this.parent[x];
+    }
+
+    public int getSize(int x) {
+        return this.size[find(x)];
+    }
+}
+
+public class MergingCommunities {
+    UnionFind uf;
+
+    public MergingCommunities(int n) {
+        this.uf = new UnionFind(n);
+    }
+
+    public void connect(int x, int y) {
+        this.uf.union(x, y);
+    }
+
+    public int getCommunitySize(int x) {
+        return this.uf.getSize(x);
+    }
+}