Added README.md file for Customer Who Visited but Did Not Make Any Tr…

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1724-customer-who-visited-but-did-not-make-any-transactions/README.md

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+<h2><a href="https://leetcode.com/problems/customer-who-visited-but-did-not-make-any-transactions">Customer Who Visited but Did Not Make Any Transactions</a></h2> <img src='https://img.shields.io/badge/Difficulty-Easy-brightgreen' alt='Difficulty: Easy' /><hr><p>Table: <code>Visits</code></p>
+
+<pre>
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| visit_id    | int     |
+| customer_id | int     |
++-------------+---------+
+visit_id is the column with unique values for this table.
+This table contains information about the customers who visited the mall.
+</pre>
+
+<p>&nbsp;</p>
+
+<p>Table: <code>Transactions</code></p>
+
+<pre>
++----------------+---------+
+| Column Name    | Type    |
++----------------+---------+
+| transaction_id | int     |
+| visit_id       | int     |
+| amount         | int     |
++----------------+---------+
+transaction_id is column with unique values for this table.
+This table contains information about the transactions made during the visit_id.
+</pre>
+
+<p>&nbsp;</p>
+
+<p>Write a&nbsp;solution to find the IDs of the users who visited without making any transactions and the number of times they made these types of visits.</p>
+
+<p>Return the result table sorted in <strong>any order</strong>.</p>
+
+<p>The&nbsp;result format is in the following example.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> 
+Visits
++----------+-------------+
+| visit_id | customer_id |
++----------+-------------+
+| 1        | 23          |
+| 2        | 9           |
+| 4        | 30          |
+| 5        | 54          |
+| 6        | 96          |
+| 7        | 54          |
+| 8        | 54          |
++----------+-------------+
+Transactions
++----------------+----------+--------+
+| transaction_id | visit_id | amount |
++----------------+----------+--------+
+| 2              | 5        | 310    |
+| 3              | 5        | 300    |
+| 9              | 5        | 200    |
+| 12             | 1        | 910    |
+| 13             | 2        | 970    |
++----------------+----------+--------+
+<strong>Output:</strong> 
++-------------+----------------+
+| customer_id | count_no_trans |
++-------------+----------------+
+| 54          | 2              |
+| 30          | 1              |
+| 96          | 1              |
++-------------+----------------+
+<strong>Explanation:</strong> 
+Customer with id = 23 visited the mall once and made one transaction during the visit with id = 12.
+Customer with id = 9 visited the mall once and made one transaction during the visit with id = 13.
+Customer with id = 30 visited the mall once and did not make any transactions.
+Customer with id = 54 visited the mall three times. During 2 visits they did not make any transactions, and during one visit they made 3 transactions.
+Customer with id = 96 visited the mall once and did not make any transactions.
+As we can see, users with IDs 30 and 96 visited the mall one time without making any transactions. Also, user 54 visited the mall twice and did not make any transactions.
+</pre>