<p>Given an integer <code>n</code>, return all the numbers in the range <code>[1, n]</code> sorted in lexicographical order.</p>

<p>You must write an algorithm that runs in&nbsp;<code>O(n)</code>&nbsp;time and uses <code>O(1)</code> extra space.&nbsp;</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> n = 13
<strong>Output:</strong> [1,10,11,12,13,2,3,4,5,6,7,8,9]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> n = 2
<strong>Output:</strong> [1,2]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 5 * 10<sup>4</sup></code></li>
</ul>

class Solution {
public:
    vector<int> lexicalOrder(int n, int currNum) {
        vector<int> currNums;

        for (int i = 0; i <= 9; i++) {
            int numToPush = currNum * 10 + i;

            if (numToPush != 0 && numToPush <= n) {
                currNums.push_back(numToPush);

                vector<int> lexical = lexicalOrder(n, numToPush);

                currNums.insert(currNums.end(), lexical.begin(), lexical.end());
            }
        }

        return currNums;
    }

    vector<int> lexicalOrder(int n) { return lexicalOrder(n, 0); }
};
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