Longest Absolute File Path LeetCode solution in Java

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class Solution {
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  public int lengthLongestPath(String input) {
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    var stack = new ArrayDeque<Integer>();
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    int max = 0;
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    String[] lines = input.split("\n");
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    for (var line : lines) {
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      int tabs = countTabs(line);
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      while (tabs < stack.size()) {
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        stack.pop();
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      }
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      int current = stack.isEmpty() ? 0 : stack.peek();
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      int nameLength = line.length() - tabs;
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      if (isFilename(line)) {
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        max = Math.max(max, current + nameLength);
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      } else {
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        stack.push(current + nameLength + 1);
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      }
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    }
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    return max;
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  }
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  private int countTabs(String s) {
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    for (int i = 0; i < s.length(); i++) {
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      if (s.charAt(i) != '\t') return i;
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    }
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    return 0;
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  }
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  private boolean isFilename(String s) {
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    return s.lastIndexOf(".") != -1;
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  }
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}