Sequential Digits
An integer has sequential digits  if and only if each digit in the number is one more than the previous digit.   Return a sorted  list of all the integers in the range [low, high]  inclusive that have sequential digits.    Example 1:  Input:  low = 100, high = 300 Output:  [123,234] Example 2:  Input:  low = 1000, high = 13000 Output:  [1234,2345,3456,4567,5678,6789,12345]   Constraints:   10 <= low <= high <= 10^9     class Solution {     public List<Integer> sequentialDigits(int low, int high) {         List<Integer> result = new ArrayList();         String str = "123456789";         int i, j, length = str.length(), num;         for( i = 2; i <= length; i++) {             for( j = 0; j <= length - i; j++) {      ...