Number of Excellent Pairs LeetCode solution in Java

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class Solution {
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  public long countExcellentPairs(int[] nums, int k) {
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    HashMap<Integer, Set<Integer>> map = new HashMap<>();
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    for (int i : nums) {
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      int x = Integer.bitCount(i);
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      map.putIfAbsent(x, new HashSet<>());
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      map.get(x).add(i);
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    }
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    long ans = 0;
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    HashSet<Integer> vis = new HashSet<>();
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    for (int i : nums) {
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      if (vis.contains(i)) continue;
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      int need = Math.max(0, k - Integer.bitCount(i));
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      for (int key : map.keySet()) // runs at max 30 times
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      if (key >= need) ans += (long) map.get(key).size();
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      vis.add(i);
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    }
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    return ans;
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  }
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}