LeetCode #1291 Sequential Digits 連續數字

public class Solution {
    public IList<int> SequentialDigits(int low, int high) {
        List<int> res = new List<int>();

        int len = low.ToString().Length;
        int highLen = high.ToString().Length;
        int startNum = 1;
        while (true) {
            if(startNum+len<=10){
                int num = genNum(startNum, len);
                if (num > high){
                    break;
                }
                if (num >= low && num <= high){
                    res.Add(num);
                }
            }
            
            if(startNum == 9){
                startNum = 1;
                len+=1;
            }
            else{
                startNum+=1;
            }

            if(len>highLen){
                break;
            }
        }

        return res;
    }

    private int genNum(int start, int length) {
        int result = 0;
        int curr = start;
        for (int i = 0; i < length; i++) {
            result = result * 10 + curr;
            if (curr == 9){
                break;
            }
            curr+=1;
        }
        return result;
    }
}