Number of Operations to Make Network Connected LeetCode solution in Java

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class Solution {
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  public int makeConnected(int n, int[][] connections) {
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    int m = connections.length;
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    if (m < n - 1) return -1;
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    UnionFind uf = new UnionFind(n);
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    for (int[] connection : connections) {
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      uf.union(connection[0], connection[1]);
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    }
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    return uf.getIsolated();
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  }
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}
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class UnionFind {
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  int[] root;
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  int[] rank;
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  int isolated;
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  public UnionFind(int n) {
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    root = new int[n];
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    rank = new int[n];
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    for (int i = 0; i < n; i++) {
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      root[i] = i;
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      rank[i] = 1;
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    }
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    isolated = 0;
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  }
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  public int find(int x) {
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    if (root[x] != x) root[x] = find(root[x]);
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    return root[x];
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  }
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  public void union(int x, int y) {
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    int rootx = find(x);
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    int rooty = find(y);
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    if (rootx == rooty) return;
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    if (rank[rootx] > rank[rooty]) {
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      root[rooty] = rootx;
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    } else if (rank[rootx] < rank[rooty]) {
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      root[rootx] = rooty;
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    } else {
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      root[rootx] = rooty;
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      rank[rooty] += 1;
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    }
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  }
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  public int getIsolated() {
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    for (int i = 0; i < root.length; i++) {
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      if (root[i] == i) isolated++;
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    }
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    return isolated - 1;
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  }
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}