Count Artifacts That Can Be Extracted LeetCode solution in Java

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class Solution {
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  public int digArtifacts(int n, int[][] artifacts, int[][] dig) {
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    HashSet<String> set = new HashSet<>();
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    for (int d[] : dig) set.add(d[0] + " " + d[1]);
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    int c = 0;
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    for (int a[] : artifacts) {
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      boolean done = true;
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      for (int i = a[0]; i <= a[2]; i++) {
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        for (int j = a[1]; j <= a[3]; j++) {
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          if (!set.contains(i + " " + j)) done = false;
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        }
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      }
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      if (done) c++;
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    }
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    return c;
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  }
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}
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// TC = O(DIG + N^2)