Added README.md file for Biggest Single Number

619-biggest-single-number/README.md

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+<h2><a href="https://leetcode.com/problems/biggest-single-number">Biggest Single Number</a></h2> <img src='https://img.shields.io/badge/Difficulty-Easy-brightgreen' alt='Difficulty: Easy' /><hr><p>Table: <code>MyNumbers</code></p>
+
+<pre>
++-------------+------+
+| Column Name | Type |
++-------------+------+
+| num         | int  |
++-------------+------+
+This table may contain duplicates (In other words, there is no primary key for this table in SQL).
+Each row of this table contains an integer.
+</pre>
+
+<p>&nbsp;</p>
+
+<p>A <strong>single number</strong> is a number that appeared only once in the <code>MyNumbers</code> table.</p>
+
+<p>Find the largest <strong>single number</strong>. If there is no <strong>single number</strong>, report <code>null</code>.</p>
+
+<p>The result format is in the following example.</p>
+<ptable> </ptable>
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> 
+MyNumbers table:
++-----+
+| num |
++-----+
+| 8   |
+| 8   |
+| 3   |
+| 3   |
+| 1   |
+| 4   |
+| 5   |
+| 6   |
++-----+
+<strong>Output:</strong> 
++-----+
+| num |
++-----+
+| 6   |
++-----+
+<strong>Explanation:</strong> The single numbers are 1, 4, 5, and 6.
+Since 6 is the largest single number, we return it.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> 
+MyNumbers table:
++-----+
+| num |
++-----+
+| 8   |
+| 8   |
+| 7   |
+| 7   |
+| 3   |
+| 3   |
+| 3   |
++-----+
+<strong>Output:</strong> 
++------+
+| num  |
++------+
+| null |
++------+
+<strong>Explanation:</strong> There are no single numbers in the input table so we return null.
+</pre>