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leetcode-problemset/leetcode/problem/percentage-of-users-attended-a-contest.html

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<p>Table: <code>Users</code></p>
<pre>
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| user_id | int |
| user_name | varchar |
+-------------+---------+
user_id is the primary key (column with unique values) for this table.
Each row of this table contains the name and the id of a user.
</pre>
<p>&nbsp;</p>
<p>Table: <code>Register</code></p>
<pre>
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| contest_id | int |
| user_id | int |
+-------------+---------+
(contest_id, user_id) is the primary key (combination of columns with unique values) for this table.
Each row of this table contains the id of a user and the contest they registered into.
</pre>
<p>&nbsp;</p>
<p>Write a solution to find the percentage of the users registered in each contest rounded to <strong>two decimals</strong>.</p>
<p>Return the result table ordered by <code>percentage</code> in <strong>descending order</strong>. In case of a tie, order it by <code>contest_id</code> in <strong>ascending order</strong>.</p>
<p>The result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong>
Users table:
+---------+-----------+
| user_id | user_name |
+---------+-----------+
| 6 | Alice |
| 2 | Bob |
| 7 | Alex |
+---------+-----------+
Register table:
+------------+---------+
| contest_id | user_id |
+------------+---------+
| 215 | 6 |
| 209 | 2 |
| 208 | 2 |
| 210 | 6 |
| 208 | 6 |
| 209 | 7 |
| 209 | 6 |
| 215 | 7 |
| 208 | 7 |
| 210 | 2 |
| 207 | 2 |
| 210 | 7 |
+------------+---------+
<strong>Output:</strong>
+------------+------------+
| contest_id | percentage |
+------------+------------+
| 208 | 100.0 |
| 209 | 100.0 |
| 210 | 100.0 |
| 215 | 66.67 |
| 207 | 33.33 |
+------------+------------+
<strong>Explanation:</strong>
All the users registered in contests 208, 209, and 210. The percentage is 100% and we sort them in the answer table by contest_id in ascending order.
Alice and Alex registered in contest 215 and the percentage is ((2/3) * 100) = 66.67%
Bob registered in contest 207 and the percentage is ((1/3) * 100) = 33.33%
</pre>