Top Competitors | HackerRank | MSSQL

The Problem

Write a query to print the respective hacker_id and name of hackers who achieved full scores for more than one challenge. Order your output in descending order by the total number of challenges in which the hacker earned a full score. If more than one hacker received full scores in same number of challenges, then sort them by ascending hacker_id.

The Input

Sample:

The Output

Sample:

90411 Joe

Explanation

1. Hacker 86870 got a score of 30 for challenge 71055 with a difficulty level of 2, so 86870 earned a full score for this challenge.
2. Hacker 90411 got a score of 30 for challenge 71055 with a difficulty level of 2, so 90411 earned a full score for this challenge.
3. Hacker 90411 got a score of 100 for challenge 66730 with a difficulty level of 6, so 90411 earned a full score for this challenge.
4. Only hacker 90411 managed to earn a full score for more than one challenge, so we print their hacker_id and name as 2 space-separated values.

The Solution

Observe the relationship across the table. From the input sample and the explanation, we can conclude that hacker_id column in Challenges table doesn't serve any purpose in this problem (purple annotations).

So, we join these 4 tables together like the following:

1. Join Submissions table with Hackers table on both hacker_id
2. Join Challenges table with Submissions table on both challenge_id
3. Join Difficulty table with Challenges table on both difficulty_level
4. Join Difficulty table with Submissions table on both score to get whoever gets the top score of each challenge

The Code

SELECT
    h.hacker_id, h.name
FROM
    hackers h
    JOIN submissions s ON h.hacker_id = s.hacker_id
    JOIN challenges c ON s.challenge_id = c.challenge_id
    JOIN difficulty d ON c.difficulty_level = d.difficulty_level AND s.score = d.score
GROUP BY
    h.hacker_id,
    h.name
HAVING
    COUNT(c.challenge_id) > 1
ORDER BY
    COUNT(c.challenge_id) DESC,
    h.hacker_id

Original Source

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