(Easy) Lexicographical Numbers - LeetCode.（非独立完成）

Description:

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:

非独自完成，思路很巧妙。

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