Count Servers that Communicate LeetCode solution in Java

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class Solution {
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  int[] parent;
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  int[] rank;
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  public int countServers(int[][] grid) {
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    parent = new int[grid.length * grid[0].length];
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    rank = new int[grid.length * grid[0].length];
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    for (int i = 0; i < parent.length; i++) {
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      parent[i] = i;
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      rank[i] = 0;
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    }
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    for (int i = 0; i < grid.length; i++) {
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      for (int j = 0; j < grid[0].length; j++) {
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        if (grid[i][j] == 1) {
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          check(i, j, grid);
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        }
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      }
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    }
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    int count = 0;
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    for (int i = 0; i < parent.length; i++) {
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      if (parent[i] != i || rank[i] > 0) {
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        count++;
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      }
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    }
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    return count;
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  }
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  public void check(int sr, int sc, int[][] grid) {
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    int mbox = sr * grid[0].length + sc;
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    for (int i = sr; i < grid.length; i++) {
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      if (grid[i][sc] == 1) {
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        int cbox = i * grid[0].length + sc;
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        int xl = find(mbox);
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        int yl = find(cbox);
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        if (xl != yl) {
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          union(xl, yl);
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        }
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      }
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    }
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    for (int j = sc; j < grid[0].length; j++) {
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      if (grid[sr][j] == 1) {
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        int cbox = sr * grid[0].length + j;
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        int xl = find(mbox);
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        int yl = find(cbox);
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        if (xl != yl) {
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          union(xl, yl);
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        }
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      }
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    }
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  }
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  int find(int x) {
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    if (parent[x] == x) {
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      return x;
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    } else {
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      parent[x] = find(parent[x]);
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      return parent[x];
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    }
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  }
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  void union(int x, int y) {
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    if (rank[x] > rank[y]) {
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      parent[y] = x;
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    } else if (rank[y] > rank[x]) {
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      parent[x] = y;
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    } else {
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      parent[x] = y;
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      rank[y]++;
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    }
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  }
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}