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Jul 5, 2025
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Added task 3601 #847

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104 changes: 104 additions & 0 deletions ...in/kotlin/g3601_3700/s3601_find_drivers_with_improved_fuel_efficiency/readme.md
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3601\. Find Drivers with Improved Fuel Efficiency

Medium

Table: `drivers`

+-------------+---------+
| Column Name | Type |
+-------------+---------+
| driver_id | int |
| driver_name | varchar |
+-------------+---------+
driver_id is the unique identifier for this table. Each row contains information about a driver.

Table: `trips`

+---------------+---------+
| Column Name | Type |
+---------------+---------+
| trip_id | int |
| driver_id | int |
| trip_date | date |
| distance_km | decimal |
| fuel_consumed | decimal |
+---------------+---------+
trip_id is the unique identifier for this table.
Each row represents a trip made by a driver, including the distance traveled and fuel consumed for that trip.

Write a solution to find drivers whose **fuel efficiency has improved** by **comparing** their average fuel efficiency in the **first half** of the year with the **second half** of the year.

* Calculate **fuel efficiency** as `distance_km / fuel_consumed` for **each** trip
* **First half**: January to June, **Second half**: July to December
* Only include drivers who have trips in **both halves** of the year
* Calculate the **efficiency improvement** as (`second_half_avg - first_half_avg`)
* **Round** all results to **`2`** decimal places

Return _the result table ordered by efficiency improvement in **descending** order, then by driver name in **ascending** order_.

The result format is in the following example.

**Example:**

**Input:**

drivers table:

+-----------+---------------+
| driver_id | driver_name |
+-----------+---------------+
| 1 | Alice Johnson |
| 2 | Bob Smith |
| 3 | Carol Davis |
| 4 | David Wilson |
| 5 | Emma Brown |
+-----------+---------------+

trips table:

+---------+-----------+------------+-------------+---------------+
| trip_id | driver_id | trip_date | distance_km | fuel_consumed |
+---------+-----------+------------+-------------+---------------+
| 1 | 1 | 2023-02-15 | 120.5 | 10.2 |
| 2 | 1 | 2023-03-20 | 200.0 | 16.5 |
| 3 | 1 | 2023-08-10 | 150.0 | 11.0 |
| 4 | 1 | 2023-09-25 | 180.0 | 12.5 |
| 5 | 2 | 2023-01-10 | 100.0 | 9.0 |
| 6 | 2 | 2023-04-15 | 250.0 | 22.0 |
| 7 | 2 | 2023-10-05 | 200.0 | 15.0 |
| 8 | 3 | 2023-03-12 | 80.0 | 8.5 |
| 9 | 3 | 2023-05-18 | 90.0 | 9.2 |
| 10 | 4 | 2023-07-22 | 160.0 | 12.8 |
| 11 | 4 | 2023-11-30 | 140.0 | 11.0 |
| 12 | 5 | 2023-02-28 | 110.0 | 11.5 |
+---------+-----------+------------+-------------+---------------+

**Output:**

+-----------+---------------+------------------+-------------------+------------------------+
| driver_id | driver_name | first_half_avg | second_half_avg | efficiency_improvement |
+-----------+---------------+------------------+-------------------+------------------------+
| 2 | Bob Smith | 11.24 | 13.33 | 2.10 |
| 1 | Alice Johnson | 11.97 | 14.02 | 2.05 |
+-----------+---------------+------------------+-------------------+------------------------+

**Explanation:**

* **Alice Johnson (driver\_id = 1):**
* First half trips (Jan-Jun): Feb 15 (120.5/10.2 = 11.81), Mar 20 (200.0/16.5 = 12.12)
* First half average efficiency: (11.81 + 12.12) / 2 = 11.97
* Second half trips (Jul-Dec): Aug 10 (150.0/11.0 = 13.64), Sep 25 (180.0/12.5 = 14.40)
* Second half average efficiency: (13.64 + 14.40) / 2 = 14.02
* Efficiency improvement: 14.02 - 11.97 = 2.05
* **Bob Smith (driver\_id = 2):**
* First half trips: Jan 10 (100.0/9.0 = 11.11), Apr 15 (250.0/22.0 = 11.36)
* First half average efficiency: (11.11 + 11.36) / 2 = 11.24
* Second half trips: Oct 5 (200.0/15.0 = 13.33)
* Second half average efficiency: 13.33
* Efficiency improvement: 13.33 - 11.24 = 2.09
* **Drivers not included:**
* Carol Davis (driver\_id = 3): Only has trips in first half (Mar, May)
* David Wilson (driver\_id = 4): Only has trips in second half (Jul, Nov)
* Emma Brown (driver\_id = 5): Only has trips in first half (Feb)

The output table is ordered by efficiency improvement in descending order then by name in ascending order.
33 changes: 33 additions & 0 deletions src/main/kotlin/g3601_3700/s3601_find_drivers_with_improved_fuel_efficiency/script.sql
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# Write your MySQL query statement below
# #Medium #Database #2025_07_05_Time_521_ms_(62.61%)_Space_0.0_MB_(100.00%)
WITH main_process AS (
SELECT
t.driver_id,
d.driver_name,
ROUND(AVG(t.distance_km / t.fuel_consumed), 2) AS first_half_avg,
ROUND(AVG(t1.distance_km / t1.fuel_consumed), 2) AS second_half_avg,
ROUND(
AVG(t1.distance_km / t1.fuel_consumed) - AVG(t.distance_km / t.fuel_consumed),
2
) AS efficiency_improvement
FROM
trips t
INNER JOIN trips t1 ON t.driver_id = t1.driver_id
INNER JOIN drivers d ON t.driver_id = d.driver_id
AND EXTRACT(MONTH FROM t.trip_date) BETWEEN 1 AND 6
AND EXTRACT(MONTH FROM t1.trip_date) BETWEEN 7 AND 12
GROUP BY
t.driver_id,
d.driver_name
ORDER BY
efficiency_improvement DESC,
d.driver_name ASC
)
SELECT
driver_id,
driver_name,
first_half_avg,
second_half_avg,
efficiency_improvement
FROM main_process
WHERE efficiency_improvement > 0;
87 changes: 87 additions & 0 deletions src/test/kotlin/g3601_3700/s3601_find_drivers_with_improved_fuel_efficiency/MysqlTest.kt
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package g3601_3700.s3601_find_drivers_with_improved_fuel_efficiency

import org.hamcrest.CoreMatchers
import org.hamcrest.MatcherAssert
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
import java.io.BufferedReader
import java.io.FileNotFoundException
import java.io.FileReader
import java.sql.SQLException
import java.util.stream.Collectors
import javax.sql.DataSource

@EmbeddedDatabaseTest(
compatibilityMode = CompatibilityMode.MySQL,
initialSqls = [
(
"CREATE TABLE drivers (driver_id INTEGER, driver_name VARCHAR(255)); " +
"INSERT INTO drivers (driver_id, driver_name) VALUES" +
"(1, 'Alice Johnson')," +
"(2, 'Bob Smith')," +
"(3, 'Carol Davis')," +
"(4, 'David Wilson')," +
"(5, 'Emma Brown');" +
"CREATE TABLE trips (trip_id INTEGER, driver_id INTEGER" +
", trip_date DATE, distance_km DECIMAL(7, 3), fuel_consumed DECIMAL(7, 3)); " +
"INSERT INTO trips (trip_id, driver_id, trip_date, distance_km, fuel_consumed) VALUES" +
"(1, 1, '2023-02-15', 120.5, 10.2)," +
"(2, 1, '2023-03-20', 200.0, 16.5)," +
"(3, 1, '2023-08-10', 150.0, 11.0)," +
"(4, 1, '2023-09-25', 180.0, 12.5)," +
"(5, 2, '2023-01-10', 100.0, 9.0)," +
"(6, 2, '2023-04-15', 250.0, 22.0)," +
"(7, 2, '2023-10-05', 200.0, 15.0)," +
"(8, 3, '2023-03-12', 80.0, 8.5)," +
"(9, 3, '2023-05-18', 90.0, 9.2)," +
"(10, 4, '2023-07-22', 160.0, 12.8)," +
"(11, 4, '2023-11-30', 140.0, 11.0)," +
"(12, 5, '2023-02-28', 110.0, 11.5);"
),
],
)
internal class MysqlTest {
@Test
@Throws(SQLException::class, FileNotFoundException::class)
fun testScript(@EmbeddedDatabase dataSource: DataSource) {
dataSource.connection.use { connection ->
connection.createStatement().use { statement ->
statement.executeQuery(
BufferedReader(
FileReader(
(
"src/main/kotlin/g3601_3700/" +
"s3601_find_drivers_with_" +
"improved_fuel_efficiency/" +
"script.sql"
),
),
)
.lines()
.collect(Collectors.joining("\n"))
.replace("#.*?\\r?\\n".toRegex(), ""),
).use { resultSet ->
MatcherAssert.assertThat<Boolean>(resultSet.next(), CoreMatchers.equalTo<Boolean>(true))
MatcherAssert.assertThat<String>(resultSet.getNString(1), CoreMatchers.equalTo<String>("2"))
MatcherAssert.assertThat<String>(
resultSet.getNString(2),
CoreMatchers.equalTo<String>("Bob Smith"),
)
MatcherAssert.assertThat<String>(resultSet.getNString(3), CoreMatchers.equalTo<String>("11.24"))
MatcherAssert.assertThat<String>(resultSet.getNString(4), CoreMatchers.equalTo<String>("13.33"))
MatcherAssert.assertThat<Boolean>(resultSet.next(), CoreMatchers.equalTo<Boolean>(true))
MatcherAssert.assertThat<String>(resultSet.getNString(1), CoreMatchers.equalTo<String>("1"))
MatcherAssert.assertThat<String>(
resultSet.getNString(2),
CoreMatchers.equalTo<String>("Alice Johnson"),
)
MatcherAssert.assertThat<String>(resultSet.getNString(3), CoreMatchers.equalTo<String>("11.97"))
MatcherAssert.assertThat<String>(resultSet.getNString(4), CoreMatchers.equalTo<String>("14.02"))
MatcherAssert.assertThat<Boolean>(resultSet.next(), CoreMatchers.equalTo<Boolean>(false))
}
}
}
}
}