> 加權 quick-union算法，是目前所有實現中最優的算法 ```java package ds.impl; import ds.UF; public class WeightedQuickUnionUF implements UF { private final int[] parent; private final int[] num; private int size; public WeightedQuickUnionUF(int n) { size = n; parent = new int[n]; num = new int[n]; for (int i = 0; i < n; i++) { parent[i] = i; num[i] = 1; } } @Override public int size() { return size; } @Override public int find(int p) { validate(p, parent.length); while (p != parent[p]) { p = parent[p]; } return p; } @Override public boolean connected(int p, int q) { return find(p) == find(q); } @Override public void union(int p, int q) { int rootP = find(p); int rootQ = find(q); if (rootP == rootQ) { return; } // make smaller root point to larger one if (num[rootP] < num[rootQ]) { parent[rootP] = rootQ; num[rootQ] += num[rootP]; } else { parent[rootQ] = rootP; num[rootP] += num[rootQ]; } size--; } } ```