Longest Uncommon Subsequence II LeetCode solution in Java

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class Solution {
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  public int findLUSlength(String[] strs) {
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    Arrays.sort(strs, (a, b) -> b.length() - a.length()); // sort descending order by length
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    // store the frequency of all strings in array
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    Map<String, Integer> map = new HashMap<>();
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    for (String s : strs) map.put(s, map.getOrDefault(s, 0) + 1);
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    for (int i = 0; i < strs.length; i++) {
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      if (map.get(strs[i]) != 1) continue; // string is not unique
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      int j;
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      for (j = 0; j < i; j++) {
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        if (isSubsequence(strs[i], strs[j])) break;
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      }
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      // if it is not a subsequence of any other larger string
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      if (j == i) return strs[i].length();
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    }
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    return -1; // no string satisfies the criterion
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  }
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  public boolean isSubsequence(String a, String b) {
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    int i = 0, j = 0;
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    while (i < a.length() && j < b.length()) if (a.charAt(i) == b.charAt(j++)) i++;
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    return i == a.length();
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  }
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}