https://leetcode.com/problems/lexicographical-numbers/description/
前20个是
1, 10, 11, 12, 13, 14, .....19 2, 20, 3, 4, 5, 6, ....9
class Solution {
public:
vector<int> lexicalOrder(int n) {
vector<int> ans;
int cur = 1;
for (int i = 1; i <= n; ++i) {
ans.push_back(cur);
if (cur * 10 <= n) {
cur *= 10;
} else if (cur % 10 != 9 && cur + 1 <= n) {
cur++;
} else {
cur += 10;
cur -= cur % 10;
while (cur % 10 == 0) cur /= 10;
}
}
return ans;
}
};