Added README.md file for Lexicographical Numbers

Author: mrprashantkumar

386-lexicographical-numbers/README.md

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+<h2><a href="https://leetcode.com/problems/lexicographical-numbers">Lexicographical Numbers</a></h2> <img src='https://img.shields.io/badge/Difficulty-Medium-orange' alt='Difficulty: Medium' /><hr><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>