content: package question1291_sequential_digits;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * 递归生成所有符合条件的数字，再排序即可。
   *
   * 时间复杂度和空间复杂度均是O(log(high))。
   *
   * 执行用时：1ms，击败64.35%。消耗内存：33.7MB，击败100.00%。
   */
  public class Solution {
      private List<Integer> result = new ArrayList<>();
  
      public List<Integer> sequentialDigits(int low, int high) {
          generateNumbers(0, low, high);
          Collections.sort(result);
          return result;
      }
  
      private void generateNumbers(int num, int low, int high) {
          if (num > high) {
              return;
          }
          if (num >= low && num <= high) {
              result.add(num);
          }
          if (num == 0) {
              for (int i = 1; i <= 9; i++) {
                  generateNumbers(i, low, high);
              }
          } else if (num % 10 < 9) {
              generateNumbers(num * 10 + num % 10 + 1, low, high);
          }
      }
  }