Leetcode: Find Median Given Frequency of Numbers

Find Median Given Frequency of Numbers

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The Numbers table keeps the value of number and its frequency.

+----------+-------------+
|  Number  |  Frequency  |
+----------+-------------|
|  0       |  7          |
|  1       |  1          |
|  2       |  3          |
|  3       |  1          |
+----------+-------------+

In this table, the numbers are 0, 0, 0, 0, 0, 0, 0, 1, 2, 2, 2, 3, so the median is (0 + 0) / 2 = 0.

+--------+
| median |
+--------|
| 0.0000 |
+--------+

Write a query to find the median of all numbers and name the result as median.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

## Blog link: https://code.dennyzhang.com/find-median-given-frequency-of-numbers
select avg(t3.Number) as median
from Numbers as t3 
inner join 
    (select t1.Number, 
        abs(sum(case when t1.Number>t2.Number then t2.Frequency else 0 end) -
            sum(case when t1.Number<t2.Number then t2.Frequency else 0 end)) as count_diff
    from numbers as t1, numbers as t2
    group by t1.Number) as t4
on t3.Number = t4.Number
where t3.Frequency>=t4.count_diff