386. 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.

给定一个int，以字典序返回小于这个int的所有值

从1开始 不断的深入递归，(1)-(10-(100-109)-   判断条件也很简单只要小于n就放到list中

public class Solution {
public List<Integer> lexicalOrder(int n) {
List<Integer> res=new ArrayList<Integer>();
for(int i=1;i<=9;i++){
dfs(i,n,res);
}
return res;
}
public void dfs(int cur,int n,List<Integer> res){
if(cur>n) return ;
res.add(cur);
for(int i=0;i<=9;i++){
dfs(cur*10+i,n,res);
}
}
}