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class Solution {
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  public String reverseWords(String s) {
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    if (s == null || s.trim().equals("")) {
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      return null;
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    }
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    String[] words = s.split(" ");
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    StringBuilder resultBuilder = new StringBuilder();
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    for (String word : words) {
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      for (int i = word.length() - 1; i >= 0; i--) {
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        resultBuilder.append(word.charAt(i));
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      }
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      resultBuilder.append(" ");
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    }
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    return resultBuilder.toString().trim();
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  }
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}