1 Description #
source: https://leetcode.com/problems/lexicographical-numbers/
Given an integer n, return all the numbers in the range [1, n] sorted in lexicographical order.
You must write an algorithm that runs in O(n) time and uses O(1) extra space.
Example 1:
Input: n = 13
Output: [1,10,11,12,13,2,3,4,5,6,7,8,9]
Example 2:
Input: n = 2
Output: [1,2]
Constraints:
1 <= n <= 5 * 10^4
2 Solution #
#include <vector>
class Solution {
public:
vector<int> lexicalOrder(int n) {
// Time complexity: O(N)
// space complexity: O(1)
int upper = std::min(9, n);
std::vector<int> result;
for (int i = 1; i <= upper; i++) {
dfs(i, n, result);
}
return result;
}
void dfs(int val, int n, std::vector<int> &result) {
if (val <= n) {
result.push_back(val);
for (int i = 0; i <= 9; i++) {
if (val * 10 + i <= n) {
dfs(val * 10 + i, n, result);
}
}
}
}
};