Number of Valid Words for Each Puzzle LeetCode solution in Java

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class Solution {
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  public List<Integer> findNumOfValidWords(String[] words, String[] puzzles) {
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    Map<Integer, Integer> map = new HashMap<>();
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    for (String w : words) {
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      int mask = 0;
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      for (int i = 0; i < w.length(); i++) {
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        mask |= 1 << (w.charAt(i) - 'a');
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      }
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      map.put(mask, map.getOrDefault(mask, 0) + 1);
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    }
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    List<Integer> res = new ArrayList<>();
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    for (String p : puzzles) {
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      int mask = 0;
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      for (int i = 0; i < p.length(); i++) {
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        mask |= 1 << (p.charAt(i) - 'a');
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      }
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      int c = 0;
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      int sub = mask;
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      int first = 1 << (p.charAt(0) - 'a');
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      while (true) {
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        if ((sub & first) == first && map.containsKey(sub)) {
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          c += map.get(sub);
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        }
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        if (sub == 0) break;
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        sub = (sub - 1) & mask; // get the next substring
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      }
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      res.add(c);
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    }
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    return res;
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  }
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}