386. Lexicographical Numbers

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386. Lexicographical Numbers

Description

Given an integer n, return all the numbers in the range [1, n] sorted in lexicographical order.

You must write an algorithm that runs inO(n)time and uses O(1) extra space.

Example 1:

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Input: n = 13
Output: [1,10,11,12,13,2,3,4,5,6,7,8,9]

Example 2:

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Input: n = 2
Output: [1,2]

Constraints:

  • 1 <= n <= 5 * 10^4

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    vector<int> res;
    int n;

    vector<int> lexicalOrder(int n) {
        this->n = n;
        for (int i = 1; i <= min(n, 9); i++) {
            dfs(i);
        }
        return res;
    }

    void dfs(int val) {
        res.push_back(val);
        for (int i = 0; i < 10; i++) {
            if (val * 10 + i > n) {
                break;
            }
            dfs(val * 10 + i);
        }
    }
};