Last Person to Fit in the Elevator

Author: Viniciuscoding

Leetcode_1204.sql

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+/*
+Last Person to Fit in the Elevator
+
+Table: Queue
+
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| person_id   | int     |
+| person_name | varchar |
+| weight      | int     |
+| turn        | int     |
++-------------+---------+
+person_id is the primary key column for this table.
+This table has the information about all people waiting for an elevator.
+The person_id and turn columns will contain all numbers from 1 to n, where n is the number of rows in the table.
+ 
+
+The maximum weight the elevator can hold is 1000.
+
+Write an SQL query to find the person_name of the last person who will fit in the elevator without exceeding the weight limit.
+It is guaranteed that the person who is first in the queue can fit in the elevator.
+
+The query result format is in the following example:
+
+Queue table
++-----------+-------------------+--------+------+
+| person_id | person_name       | weight | turn |
++-----------+-------------------+--------+------+
+| 5         | George Washington | 250    | 1    |
+| 3         | John Adams        | 350    | 2    |
+| 6         | Thomas Jefferson  | 400    | 3    |
+| 2         | Will Johnliams    | 200    | 4    |
+| 4         | Thomas Jefferson  | 175    | 5    |
+| 1         | James Elephant    | 500    | 6    |
++-----------+-------------------+--------+------+
+
+Result table
++-------------------+
+| person_name       |
++-------------------+
+| Thomas Jefferson  |
++-------------------+
+
+Queue table is ordered by turn in the example for simplicity.
+In the example George Washington(id 5), John Adams(id 3) and Thomas Jefferson(id 6) will enter the elevator as their 
+weight sum is 250 + 350 + 400 = 1000. Thomas Jefferson(id 6) is the last person to fit in the elevator because he has the
+last turn in these three people.
+*/
+
+# MY SOLUTION
+SELECT c.person_name
+FROM (SELECT a.person_name, SUM(b.weight) AS maximum
+      FROM (SELECT person_id * 0 AS grouping, person_name, weight, turn
+            FROM Queue) AS a
+      INNER JOIN (SELECT person_id * 0 AS grouping, person_name, weight, turn
+                  FROM Queue) AS b
+      ON a.grouping = b.grouping AND a.turn >= b.turn
+      GROUP BY a.grouping, a.turn
+      HAVING maximum <= 1000
+      ORDER BY a.turn DESC) AS c
+LIMIT 1
+
+# SOLUTION by LijianChen
+SELECT a.person_name
+FROM Queue a
+INNER JOIN Queue b
+ON a.turn >= b.turn
+GROUP BY a.turn
+HAVING SUM(b.weight) <= 1000
+ORDER BY SUM(b.weight) DESC
+LIMIT 1