quickunion.java

public class QuickUnionUF {
    private int[] parent; 
    private int count; 

 public QuickUnionUF(int n) {
        parent = new int[n];
        count = n;
        for (int i = 0; i < n; i++) {
            parent[i] = i;
        }

}
public int count() {
        return count;
    }
 public int find(int p) {
        validate(p);
        while (p != parent[p])
            p = parent[p];
        return p;
    }
private void validate(int p) {
        int n = parent.length;
        if (p < 0 || p >= n) {
            throw new IllegalArgumentException("index " + p + " is not between 0 and " + (n-1));
        }
    }
 @Deprecated
    public boolean connected(int p, int q) {
        return find(p) == find(q);
    }

 public void union(int p, int q) {
        int rootP = find(p);
        int rootQ = find(q);
        if (rootP == rootQ) return;
        parent[rootP] = rootQ; 
        count--;
    }
    public static void main(String[] args) {
        int n = StdIn.readInt();
        QuickUnionUF uf = new QuickUnionUF(n);
        while (!StdIn.isEmpty()) {
            int p = StdIn.readInt();
            int q = StdIn.readInt();
            if (uf.find(p) == uf.find(q)) continue;
            uf.union(p, q);
            StdOut.println(p + " " + q);
        }
        StdOut.println(uf.count() + " components");
    }


}