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  • src
    • main/kotlin/g3601_3700/s3601_find_drivers_with_improved_fuel_efficiency
    • test/kotlin/g3601_3700/s3601_find_drivers_with_improved_fuel_efficiency

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‎src/main/kotlin/g3601_3700/s3601_find_drivers_with_improved_fuel_efficiency/readme.md‎

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3601\. Find Drivers with Improved Fuel Efficiency
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Medium
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Table: `drivers`
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+-------------+---------+
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| Column Name | Type |
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+-------------+---------+
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| driver_id | int |
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| driver_name | varchar |
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+-------------+---------+
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driver_id is the unique identifier for this table. Each row contains information about a driver.
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Table: `trips`
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+---------------+---------+
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| Column Name | Type |
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+---------------+---------+
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| trip_id | int |
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| driver_id | int |
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| trip_date | date |
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| distance_km | decimal |
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| fuel_consumed | decimal |
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+---------------+---------+
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trip_id is the unique identifier for this table.
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Each row represents a trip made by a driver, including the distance traveled and fuel consumed for that trip.
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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.
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* Calculate **fuel efficiency** as `distance_km / fuel_consumed` for **each** trip
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* **First half**: January to June, **Second half**: July to December
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* Only include drivers who have trips in **both halves** of the year
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* Calculate the **efficiency improvement** as (`second_half_avg - first_half_avg`)
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* **Round** all results to **`2`** decimal places
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Return _the result table ordered by efficiency improvement in **descending** order, then by driver name in **ascending** order_.
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The result format is in the following example.
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**Example:**
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**Input:**
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drivers table:
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+-----------+---------------+
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| driver_id | driver_name |
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+-----------+---------------+
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| 1 | Alice Johnson |
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| 2 | Bob Smith |
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| 3 | Carol Davis |
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| 4 | David Wilson |
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| 5 | Emma Brown |
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+-----------+---------------+
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trips table:
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+---------+-----------+------------+-------------+---------------+
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| trip_id | driver_id | trip_date | distance_km | fuel_consumed |
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+---------+-----------+------------+-------------+---------------+
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| 1 | 1 | 2023-02-15 | 120.5 | 10.2 |
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| 2 | 1 | 2023-03-20 | 200.0 | 16.5 |
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| 3 | 1 | 2023-08-10 | 150.0 | 11.0 |
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| 4 | 1 | 2023-09-25 | 180.0 | 12.5 |
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| 5 | 2 | 2023-01-10 | 100.0 | 9.0 |
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| 6 | 2 | 2023-04-15 | 250.0 | 22.0 |
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| 7 | 2 | 2023-10-05 | 200.0 | 15.0 |
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| 8 | 3 | 2023-03-12 | 80.0 | 8.5 |
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| 9 | 3 | 2023-05-18 | 90.0 | 9.2 |
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| 10 | 4 | 2023-07-22 | 160.0 | 12.8 |
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| 11 | 4 | 2023-11-30 | 140.0 | 11.0 |
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| 12 | 5 | 2023-02-28 | 110.0 | 11.5 |
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+---------+-----------+------------+-------------+---------------+
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**Output:**
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+-----------+---------------+------------------+-------------------+------------------------+
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| driver_id | driver_name | first_half_avg | second_half_avg | efficiency_improvement |
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+-----------+---------------+------------------+-------------------+------------------------+
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| 2 | Bob Smith | 11.24 | 13.33 | 2.10 |
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| 1 | Alice Johnson | 11.97 | 14.02 | 2.05 |
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+-----------+---------------+------------------+-------------------+------------------------+
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**Explanation:**
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* **Alice Johnson (driver\_id = 1):**
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* First half trips (Jan-Jun): Feb 15 (120.5/10.2 = 11.81), Mar 20 (200.0/16.5 = 12.12)
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* First half average efficiency: (11.81 + 12.12) / 2 = 11.97
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* Second half trips (Jul-Dec): Aug 10 (150.0/11.0 = 13.64), Sep 25 (180.0/12.5 = 14.40)
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* Second half average efficiency: (13.64 + 14.40) / 2 = 14.02
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* Efficiency improvement: 14.02 - 11.97 = 2.05
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* **Bob Smith (driver\_id = 2):**
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* First half trips: Jan 10 (100.0/9.0 = 11.11), Apr 15 (250.0/22.0 = 11.36)
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* First half average efficiency: (11.11 + 11.36) / 2 = 11.24
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* Second half trips: Oct 5 (200.0/15.0 = 13.33)
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* Second half average efficiency: 13.33
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* Efficiency improvement: 13.33 - 11.24 = 2.09
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* **Drivers not included:**
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* Carol Davis (driver\_id = 3): Only has trips in first half (Mar, May)
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* David Wilson (driver\_id = 4): Only has trips in second half (Jul, Nov)
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* Emma Brown (driver\_id = 5): Only has trips in first half (Feb)
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The output table is ordered by efficiency improvement in descending order then by name in ascending order.

‎src/main/kotlin/g3601_3700/s3601_find_drivers_with_improved_fuel_efficiency/script.sql‎

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# Write your MySQL query statement below
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# #Medium #Database #2025_07_05_Time_521_ms_(62.61%)_Space_0.0_MB_(100.00%)
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WITH main_process AS (
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SELECT
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t.driver_id,
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d.driver_name,
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ROUND(AVG(t.distance_km / t.fuel_consumed), 2) AS first_half_avg,
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ROUND(AVG(t1.distance_km / t1.fuel_consumed), 2) AS second_half_avg,
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ROUND(
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AVG(t1.distance_km / t1.fuel_consumed) - AVG(t.distance_km / t.fuel_consumed),
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2
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) AS efficiency_improvement
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FROM
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trips t
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INNER JOIN trips t1 ON t.driver_id = t1.driver_id
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INNER JOIN drivers d ON t.driver_id = d.driver_id
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AND EXTRACT(MONTH FROM t.trip_date) BETWEEN 1 AND 6
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AND EXTRACT(MONTH FROM t1.trip_date) BETWEEN 7 AND 12
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GROUP BY
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t.driver_id,
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d.driver_name
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ORDER BY
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efficiency_improvement DESC,
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d.driver_name ASC
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)
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SELECT
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driver_id,
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driver_name,
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first_half_avg,
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second_half_avg,
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efficiency_improvement
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FROM main_process
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WHERE efficiency_improvement > 0;

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

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