Letter Tile Possibilities LeetCode solution in Java

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class Solution {
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  private int result = 0;
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  public int numTilePossibilities(String tiles) {
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    Map<Character, Integer> map = new HashMap<>();
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    for (char c : tiles.toCharArray()) {
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      map.put(c, map.getOrDefault(c, 0) + 1);
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    }
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    find(map);
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    return result - 1;
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  }
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  public void find(Map<Character, Integer> map) {
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    result++;
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    for (Map.Entry<Character, Integer> m : map.entrySet()) {
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      char c = m.getKey();
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      int val = m.getValue();
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      if (val > 0) {
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        map.put(c, val - 1);
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        find(map);
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        map.put(c, val);
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      }
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    }
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  }
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}