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leetcode-cn/problem (English)/查找类别推荐对(English) [find-category-recommendation-pairs].html Normal file
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<p>Table: <code>ProductPurchases</code></p>
<pre>
+-------------+------+
| Column Name | Type |
+-------------+------+
| user_id | int |
| product_id | int |
| quantity | int |
+-------------+------+
(user_id, product_id) is the unique identifier for this table.
Each row represents a purchase of a product by a user in a specific quantity.
</pre>
<p>Table: <code>ProductInfo</code></p>
<pre>
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| product_id | int |
| category | varchar |
| price | decimal |
+-------------+---------+
product_id is the unique identifier for this table.
Each row assigns a category and price to a product.
</pre>
<p>Amazon wants to understand shopping patterns across product categories. Write a solution to:</p>
<ol>
<li>Find all <strong>category pairs</strong> (where <code>category1</code> &lt; <code>category2</code>)</li>
<li>For <strong>each category pair</strong>, determine the number of <strong>unique</strong> <strong>customers</strong> who purchased products from <strong>both</strong> categories</li>
</ol>
<p>A category pair is considered <strong>reportable</strong> if at least <code>3</code> different customers have purchased products from both categories.</p>
<p>Return <em>the result table of reportable category pairs ordered by <strong>customer_count</strong> in <strong>descending</strong> order, and in case of a tie, by <strong>category1</strong> in <strong>ascending</strong> order lexicographically, and then by <strong>category2</strong> in <strong>ascending</strong> order.</em></p>
<p>The result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example:</strong></p>
<div class="example-block">
<p><strong>Input:</strong></p>
<p>ProductPurchases table:</p>
<pre class="example-io">
+---------+------------+----------+
| user_id | product_id | quantity |
+---------+------------+----------+
| 1 | 101 | 2 |
| 1 | 102 | 1 |
| 1 | 201 | 3 |
| 1 | 301 | 1 |
| 2 | 101 | 1 |
| 2 | 102 | 2 |
| 2 | 103 | 1 |
| 2 | 201 | 5 |
| 3 | 101 | 2 |
| 3 | 103 | 1 |
| 3 | 301 | 4 |
| 3 | 401 | 2 |
| 4 | 101 | 1 |
| 4 | 201 | 3 |
| 4 | 301 | 1 |
| 4 | 401 | 2 |
| 5 | 102 | 2 |
| 5 | 103 | 1 |
| 5 | 201 | 2 |
| 5 | 202 | 3 |
+---------+------------+----------+
</pre>
<p>ProductInfo table:</p>
<pre class="example-io">
+------------+-------------+-------+
| product_id | category | price |
+------------+-------------+-------+
| 101 | Electronics | 100 |
| 102 | Books | 20 |
| 103 | Books | 35 |
| 201 | Clothing | 45 |
| 202 | Clothing | 60 |
| 301 | Sports | 75 |
| 401 | Kitchen | 50 |
+------------+-------------+-------+
</pre>
<p><strong>Output:</strong></p>
<pre class="example-io">
+-------------+-------------+----------------+
| category1 | category2 | customer_count |
+-------------+-------------+----------------+
| Books | Clothing | 3 |
| Books | Electronics | 3 |
| Clothing | Electronics | 3 |
| Electronics | Sports | 3 |
+-------------+-------------+----------------+
</pre>
<p><strong>Explanation:</strong></p>
<ul>
<li><strong>Books-Clothing</strong>:
<ul>
<li>User 1 purchased products from Books (102) and Clothing (201)</li>
<li>User 2 purchased products from Books (102, 103) and Clothing (201)</li>
<li>User 5 purchased products from Books (102, 103) and Clothing (201, 202)</li>
<li>Total: 3 customers purchased from both categories</li>
</ul>
</li>
<li><strong>Books-Electronics</strong>:
<ul>
<li>User 1 purchased products from Books (102) and Electronics (101)</li>
<li>User 2 purchased products from Books (102, 103) and Electronics (101)</li>
<li>User 3 purchased products from Books (103) and Electronics (101)</li>
<li>Total: 3 customers purchased from both categories</li>
</ul>
</li>
<li><strong>Clothing-Electronics</strong>:
<ul>
<li>User 1 purchased products from Clothing (201) and Electronics (101)</li>
<li>User 2 purchased products from Clothing (201) and Electronics (101)</li>
<li>User 4 purchased products from Clothing (201) and Electronics (101)</li>
<li>Total: 3 customers purchased from both categories</li>
</ul>
</li>
<li><strong>Electronics-Sports</strong>:
<ul>
<li>User 1 purchased products from Electronics (101) and Sports (301)</li>
<li>User 3 purchased products from Electronics (101) and Sports (301)</li>
<li>User 4 purchased products from Electronics (101) and Sports (301)</li>
<li>Total: 3 customers purchased from both categories</li>
</ul>
</li>
<li>Other category pairs like Clothing-Sports (only 2 customers: Users 1 and 4) and Books-Kitchen (only 1 customer: User 3) have fewer than 3 shared customers and are not included in the result.</li>
</ul>
<p>The result is ordered by customer_count in descending order. Since all pairs have the same customer_count of 3, they are ordered by category1 (then category2) in ascending order.</p>
</div>