leetcode386. 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.

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