SELECT A.submission_date, A.unique_hackers, B.top_hacker_id, B.name
FROM

(SELECT submission_date AS submission_date, SUM(unique_hackers) AS unique_hackers FROM
    (SELECT s1.submission_date AS submission_date, COUNT(DISTINCT s2.hacker_id) AS unique_hackers
    FROM Submissions s1 JOIN Submissions s2
    ON s2.submission_date <= s1.submission_date
    GROUP BY s1.submission_date, s2.hacker_id
    HAVING COUNT(DISTINCT s2.submission_date) = DAY(s1.submission_date)
    ORDER BY s1.submission_date) uk
GROUP BY submission_date 
ORDER BY submission_date) A

JOIN

(SELECT t.submission_date AS submission_date, t.top_hacker_id AS top_hacker_id, h.name AS name
FROM
(SELECT s3.submission_date AS submission_date, 
    (SELECT hacker_id FROM Submissions s4
     WHERE s4.submission_date = s3.submission_date
     GROUP BY s4.hacker_id
     ORDER BY COUNT(s4.submission_id) DESC, s4.hacker_id 
     LIMIT 1) AS top_hacker_id
 FROM Submissions s3
 GROUP BY s3.submission_date) t 
JOIN Hackers h
ON t.top_hacker_id = h.hacker_id
ORDER BY t.submission_date) B

ON A.submission_date = B.submission_date
ORDER BY A.submission_date;