Find the person_name of the last person that can fit on the bus without exceeding the weight limit of 1000.
This challenge now meets the current minimum standard for sitemap inclusion and independent indexing.
Find the person_name of the last person that can fit on the bus without exceeding the weight limit of 1000.
Running totals are one of the most useful window-function patterns in analytics and operations. The exact shape appears in capacity planning, inventory thresholds, credit exposure checks, and any sequence where you need to know the last safe row before crossing a limit.
person_idperson_nameweightturnWITH queue_weights AS (
SELECT
person_name,
turn,
SUM(weight) OVER (ORDER BY turn) AS cum_weight
FROM queue
)
SELECT
person_name
FROM queue_weights
WHERE cum_weight <= 1000
ORDER BY cum_weight DESC
LIMIT 1This is the standard solution. The window SUM builds the running weight by boarding order, and the final filter keeps only the feasible passengers before selecting the latest one.
SELECT
q1.person_name
FROM queue q1
WHERE (
SELECT SUM(q2.weight)
FROM queue q2
WHERE q2.turn <= q1.turn
) <= 1000
ORDER BY q1.turn DESC
LIMIT 1This version avoids window functions and can help explain the logic from first principles. It is less efficient on larger tables, but it makes the cumulative condition very explicit.
The main mistake is ordering by weight instead of by turn. The constraint is about boarding sequence, so the running total must follow turn order exactly. Another bug is choosing the maximum single weight under 1000 instead of the last cumulative total under 1000.
Because the bus fills in queue order, not by passenger weight. The cumulative sum must follow the boarding sequence or the answer no longer reflects the real process.
It teaches running totals with window functions: keeping row-level detail while also carrying forward an ordered cumulative metric.
Use these guides when you want the fuller explanation behind the SQL pattern this challenge is testing.
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