Increasing Decreasing String LeetCode solution in Java

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class Solution {
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  public String sortString(String s) {
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    StringBuilder result = new StringBuilder();
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    int[] freq = new int[26];
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    for (char c : s.toCharArray()) {
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      freq[c - 'a']++;
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    }
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    int remaining = s.length();
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    while (remaining != 0) {
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      for (int i = 0; i < 26 && remaining != 0; i++) {
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        if (freq[i] != 0) {
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          freq[i]--;
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          result.append((char) (i + 'a'));
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          remaining--;
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        }
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      }
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      for (int i = 25; i >= 0 && remaining != 0; i--) {
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        if (freq[i] != 0) {
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          freq[i]--;
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          result.append((char) (i + 'a'));
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          remaining--;
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        }
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      }
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    }
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    return result.toString();
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  }
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}