LeetCode——Consecutive Numbers

Description:

Write a SQL query to find all numbers that appear at least three times consecutively.

+----+-----+
| Id | Num |
+----+-----+
| 1  |  1  |
| 2  |  1  |
| 3  |  1  |
| 4  |  2  |
| 5  |  1  |
| 6  |  2  |
| 7  |  2  |
+----+-----+

For example, given the above Logs table, 1 is the only number that appears consecutively for at least three times.

要查出连续至少出现3次的Num。需要3个循环套一起，但是时间复杂度是O(n)，因为每个循环实际上只遍历了一次。

# Write your MySQL query statement below
select DISTINCT(l1.Num)
from Logs l1, Logs l2, Logs l3
where l1.Id+1=l2.Id and l1.Id+2=l3.Id and l1.Num=l2.Num and l1.Num=l3.Num;