Detect Squares LeetCode solution in Java

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class DetectSquares {
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  List<int[]> coordinates;
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  Map<String, Integer> counts;
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  public DetectSquares() {
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    coordinates = new ArrayList<>();
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    counts = new HashMap<>();
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  }
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  public void add(int[] point) {
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    coordinates.add(point);
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    String key = point[0] + "@" + point[1];
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    counts.put(key, counts.getOrDefault(key, 0) + 1);
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  }
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  public int count(int[] point) {
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    int sum = 0, px = point[0], py = point[1];
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    for (int[] coordinate : coordinates) {
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      int x = coordinate[0], y = coordinate[1];
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      if (px == x || py == y || (Math.abs(px - x) != Math.abs(py - y))) continue;
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      sum += counts.getOrDefault(x + "@" + py, 0) * counts.getOrDefault(px + "@" + y, 0);
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    }
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    return sum;
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  }
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}