1public class Solution {
2    public int MakeConnected(int n, int[][] connections) {
3        if (connections.Length < n - 1) return -1;
4
5        int[] parent = new int[n];
6        int[] rank = new int[n];
7        for (int i = 0; i < n; i++) parent[i] = i;
8
9        foreach (var conn in connections) {
10            Union(parent, rank, conn[0], conn[1]);
11        }
12
13        int components = 0;
14        for (int i = 0; i < n; i++) {
            if (Find(parent, i) == i) components++;
        }
        
        return components - 1;
    }

    private int Find(int[] parent, int i) {
        if (parent[i] != i) {
            parent[i] = Find(parent, parent[i]);
        }
        return parent[i];
    }

    private void Union(int[] parent, int[] rank, int x, int y) {
        int rootX = Find(parent, x);
        int rootY = Find(parent, y);
        if (rootX != rootY) {
            if (rank[rootX] < rank[rootY]) {
                parent[rootX] = rootY;
            } else if (rank[rootX] > rank[rootY]) {
                parent[rootY] = rootX;
            } else {
                parent[rootY] = rootX;
                rank[rootX]++;
            }
        }
    }
}