WITH 
cte0 AS( --Join of tables (Creating Master Table).
    SELECT s.submission_date, s.submission_id, s.hacker_id, h.name
    FROM submissions s
    LEFT JOIN hackers h ON s.hacker_id = h.hacker_id
    WHERE s.submission_date BETWEEN '2016-03-01' AND '2016-03-15'),
cte1 AS( --Date & Sequence
    SELECT 
        submission_date,
        ROW_NUMBER() OVER(ORDER BY submission_date ASC) AS dt_seq
    FROM cte0
    GROUP BY submission_date),
cte2 AS( --All hackers with at least one submission.
    SELECT hacker_id, submission_date, COUNT(submission_id) AS sb_count
    FROM cte0
    GROUP BY hacker_id, submission_date
    HAVING COUNT(submission_id)>0),
cte3 AS( --All hackers with at least one submission each day.
    SELECT 
        hacker_id, submission_date,
        ROW_NUMBER() OVER(PARTITION BY hacker_id ORDER BY submission_date) AS h_seq
    FROM cte2),
cte4 AS ( -- result of first query
    SELECT cte3.submission_date, COUNT(hacker_id) AS num_hackers
    FROM cte3
    JOIN cte1 ON cte1.submission_date = cte3.submission_date AND cte1.dt_seq = cte3.h_seq
    GROUP BY cte3.submission_date),
cte5 AS ( 
    SELECT 
        submission_date, hacker_id,
        RANK() OVER(PARTITION BY submission_date ORDER BY sb_count DESC, hacker_id ASC) AS rnk
    FROM cte2),
cte6 AS ( -- result of 2nd query
    SELECT submission_date, hacker_id 
    FROM cte5 
    WHERE rnk=1),
cte7 AS (
    SELECT hacker_id, name
    FROM cte0
    GROUP BY hacker_id, name)

SELECT cte4.submission_date, cte4.num_hackers, cte6.hacker_id, cte7.name
FROM cte4
JOIN cte6 ON cte6.submission_date = cte4.submission_date
JOIN cte7 ON cte7.hacker_id = cte6.hacker_id
ORDER BY cte4.submission_date;