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class Solution {
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  public List<Integer> sequentialDigits(int low, int high) {
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    int lowSize = String.valueOf(low).length(), highSize = String.valueOf(high).length();
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    List<Integer> output = new ArrayList<>();
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    for (int size = lowSize; size <= highSize; size++) {
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      int seedNumber = getSeedNumber(size);
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      int increment = getIncrement(size);
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      int limit = (int) Math.pow(10, size);
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      // System.out.println(seedNumber+":"+increment+":"+limit);
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      while (true) {
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        if (seedNumber >= low && seedNumber <= high) output.add(seedNumber);
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        if (seedNumber % 10 == 9 || seedNumber > high) break;
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        seedNumber += increment;
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      }
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    }
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    return output;
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  }
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  private int getSeedNumber(int size) {
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    int seed = 1;
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    for (int i = 2; i <= size; i++) seed = 10 * seed + i;
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    return seed;
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  }
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  private int getIncrement(int size) {
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    int increment = 1;
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    for (int i = 2; i <= size; i++) increment = 10 * increment + 1;
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    return increment;
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  }
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}