[leetcode] 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.

解法一：

大神方法，O(n) time O(1) space。

class Solution
4000
{
public:
vector<int> lexicalOrder(int n) {
if (n < 1) return vector<int>();
vector<int> result(n);
result[0] = 1;
for (int i = 1; i < n; ++ i)
result[i] = next(result[i - 1], n);
return result;
}

int next(int last, int n)
{
if (last * 10 <= n)
return last * 10;
if (last == n)
last /= 10;
++last;
while(last % 10 == 0)
last /= 10;
return last;
}
};