Lexicographical Numbers

Given an integer n, return 1 - n in lexicographical order.

For example, given 13, return: [1,10,11,12,13,2,3,4,5,6,7,8,9].

Please optimize your algorithm to use less time and space. The input size may be as large as 5,000,000.

Solution:

public class Solution {
    public List<Integer> lexicalOrder(int n) {
        List<Integer> ans = new ArrayList<>();
        int cur = 1;
        for(int i=0; i<n; i++){
            ans.add(cur);
            if(cur*10<=n) cur *= 10;
            else if(cur%10!=9 && cur+1<=n) cur += 1;
            else {
                while((cur/10)%10==9) cur /= 10;
                cur = cur / 10 + 1;
            }
        }
        return ans;
    }
}