1291. Sequential Digits

Python

Time: O(1)

Space: O(1)

class Solution:
    def sequentialDigits(self, low: int, high: int) -> List[int]:
        digits = [str(digit) for digit in range(1, 10)]
        
        result = []
        
        for i in range(0, 9):
            for j in range(i, 9):
                num = int(''.join(digits[i:j+1]))
                if num >= low and num <= high:
                    result.append(num)
                
        return sorted(result)