leetcode 打印从1到最大的n位数

书上原题本想考的是大数问题，但是leetcode上要求的返回值是int，不可能出现当n过大时大数越界的问题， 失去了本题的意义。按大数问题处理，用string和递归来处理该问题。

public class Solution {
    public int[] PrintNumbers(int n) 
    {
        List resList = new List();
        char[] bigNumber = new char[n];
        DFS(0, n, ref bigNumber, resList);
        if(resList.Contains(0))
            resList.Remove(0);
        return resList.ToArray();
    }


    private void DFS(int n, int target, ref char[]bigNumber, List resList)
    {
        if(n == target)
        {
            string s = new string(bigNumber);
            resList.Add(int.Parse(s));
            return;
        }
        for(int i = 0 ; i < 10; i++)
        {
            bigNumber[n] = char.Parse( i.ToString() );
            DFS(n + 1, target, ref bigNumber, resList);
        }
    }
    
}