Added task 3554

src/main/java/g3501_3600/s3554_find_category_recommendation_pairs/readme.md

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+3554\. Find Category Recommendation Pairs
+
+Table: `ProductPurchases`
+
+    +-------------+------+
+    | 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. 
+
+Table: `ProductInfo`
+
+    +-------------+---------+
+    | 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. 
+
+Amazon wants to understand shopping patterns across product categories. Write a solution to:
+
+1.  Find all **category pairs** (where `category1` < `category2`)
+2.  For **each category pair**, determine the number of **unique** **customers** who purchased products from **both** categories
+
+A category pair is considered **reportable** if at least `3` different customers have purchased products from both categories.
+
+Return _the result table of reportable category pairs ordered by **customer\_count** in **descending** order, and in case of a tie, by **category1** in **ascending** order lexicographically, and then by **category2** in **ascending** order._
+
+The result format is in the following example.
+
+**Example:**
+
+**Input:**
+
+ProductPurchases table:
+
+    +---------+------------+----------+
+    | 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        | 
+    +---------+------------+----------+ 
+
+ProductInfo table:
+
+    +------------+-------------+-------+
+    | 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    |
+    +------------+-------------+-------+ 
+
+**Output:**
+
+    +-------------+-------------+----------------+
+    | category1   | category2   | customer_count |
+    +-------------+-------------+----------------+
+    | Books       | Clothing    | 3              |
+    | Books       | Electronics | 3              |
+    | Clothing    | Electronics | 3              |
+    | Electronics | Sports      | 3              |
+    +-------------+-------------+----------------+ 
+
+**Explanation:**
+
+*   **Books-Clothing**:
+    *   User 1 purchased products from Books (102) and Clothing (201)
+    *   User 2 purchased products from Books (102, 103) and Clothing (201)
+    *   User 5 purchased products from Books (102, 103) and Clothing (201, 202)
+    *   Total: 3 customers purchased from both categories
+*   **Books-Electronics**:
+    *   User 1 purchased products from Books (102) and Electronics (101)
+    *   User 2 purchased products from Books (102, 103) and Electronics (101)
+    *   User 3 purchased products from Books (103) and Electronics (101)
+    *   Total: 3 customers purchased from both categories
+*   **Clothing-Electronics**:
+    *   User 1 purchased products from Clothing (201) and Electronics (101)
+    *   User 2 purchased products from Clothing (201) and Electronics (101)
+    *   User 4 purchased products from Clothing (201) and Electronics (101)
+    *   Total: 3 customers purchased from both categories
+*   **Electronics-Sports**:
+    *   User 1 purchased products from Electronics (101) and Sports (301)
+    *   User 3 purchased products from Electronics (101) and Sports (301)
+    *   User 4 purchased products from Electronics (101) and Sports (301)
+    *   Total: 3 customers purchased from both categories
+*   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.
+
+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.

src/main/java/g3501_3600/s3554_find_category_recommendation_pairs/script.sql

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+# Write your MySQL query statement below
+# #Hard #Database #2025_05_22_Time_623_ms_(82.76%)_Space_0.0_MB_(100.00%)
+SELECT
+    pi1.category AS category1,
+    pi2.category AS category2,
+    COUNT(DISTINCT pp1.user_id) AS customer_count
+FROM
+    ProductPurchases pp1,
+    ProductPurchases pp2,
+    ProductInfo pi1,
+    ProductInfo pi2
+WHERE
+    pp1.user_id = pp2.user_id
+    AND pi1.category < pi2.category
+    AND pp1.product_id = pi1.product_id
+    AND pp2.product_id = pi2.product_id
+GROUP BY
+    pi1.category,
+    pi2.category
+HAVING
+    COUNT(DISTINCT pp1.user_id) >= 3
+ORDER BY
+    customer_count DESC,
+    category1 ASC,
+    category2 ASC;

src/test/java/g3501_3600/s3554_find_category_recommendation_pairs/MysqlTest.java

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+package g3501_3600.s3554_find_category_recommendation_pairs;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import java.io.BufferedReader;
+import java.io.FileNotFoundException;
+import java.io.FileReader;
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.stream.Collectors;
+import javax.sql.DataSource;
+import org.junit.jupiter.api.Test;
+import org.zapodot.junit.db.annotations.EmbeddedDatabase;
+import org.zapodot.junit.db.annotations.EmbeddedDatabaseTest;
+import org.zapodot.junit.db.common.CompatibilityMode;
+
+@EmbeddedDatabaseTest(
+        compatibilityMode = CompatibilityMode.MySQL,
+        initialSqls =
+                "CREATE TABLE ProductPurchases(user_id INTEGER, product_id INTEGER"
+                        + ", quantity INTEGER); "
+                        + "INSERT INTO ProductPurchases(user_id, product_id, quantity)"
+                        + " VALUES "
+                        + "(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);"
+                        + "CREATE TABLE ProductInfo(product_id INTEGER, category VARCHAR(255)"
+                        + ", price INTEGER); "
+                        + "INSERT INTO ProductInfo(product_id, category, price) VALUES "
+                        + "(101, 'Electronics', 100), "
+                        + "(102, 'Books', 20), "
+                        + "(103, 'Books', 35), "
+                        + "(201, 'Clothing', 45), "
+                        + "(202, 'Clothing', 60), "
+                        + "(301, 'Sports', 75), "
+                        + "(401, 'Kitchen', 50);")
+class MysqlTest {
+    @Test
+    void testScript(@EmbeddedDatabase DataSource dataSource)
+            throws SQLException, FileNotFoundException {
+        try (final Connection connection = dataSource.getConnection()) {
+            try (final Statement statement = connection.createStatement();
+                    final ResultSet resultSet =
+                            statement.executeQuery(
+                                    new BufferedReader(
+                                                    new FileReader(
+                                                            "src/main/java/g3501_3600/"
+                                                                    + "s3554_find_category_recommendation_pairs/"
+                                                                    + "script.sql"))
+                                            .lines()
+                                            .collect(Collectors.joining("\n"))
+                                            .replaceAll("#.*?\\r?\\n", ""))) {
+                assertThat(resultSet.next(), equalTo(true));
+                assertThat(resultSet.getNString(1), equalTo("Books"));
+                assertThat(resultSet.getNString(2), equalTo("Clothing"));
+                assertThat(resultSet.getNString(3), equalTo("3"));
+                assertThat(resultSet.next(), equalTo(true));
+                assertThat(resultSet.getNString(1), equalTo("Books"));
+                assertThat(resultSet.getNString(2), equalTo("Electronics"));
+                assertThat(resultSet.getNString(3), equalTo("3"));
+                assertThat(resultSet.next(), equalTo(true));
+                assertThat(resultSet.getNString(1), equalTo("Clothing"));
+                assertThat(resultSet.getNString(2), equalTo("Electronics"));
+                assertThat(resultSet.getNString(3), equalTo("3"));
+                assertThat(resultSet.next(), equalTo(true));
+                assertThat(resultSet.getNString(1), equalTo("Electronics"));
+                assertThat(resultSet.getNString(2), equalTo("Sports"));
+                assertThat(resultSet.getNString(3), equalTo("3"));
+                assertThat(resultSet.next(), equalTo(false));
+            }
+        }
+    }
+}