Consecutive Numbers

LeetCode 180 | Difficulty: Medium

Medium

Problem Description

Table: Logs

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| num         | varchar |
+-------------+---------+
In SQL, id is the primary key for this table.
id is an autoincrement column starting from 1.

Find all numbers that appear at least three times consecutively.

Return the result table in any order.

The result format is in the following example.

Example 1:

Input: 
Logs table:
+----+-----+
| id | num |
+----+-----+
| 1  | 1   |
| 2  | 1   |
| 3  | 1   |
| 4  | 2   |
| 5  | 1   |
| 6  | 2   |
| 7  | 2   |
+----+-----+
Output: 
+-----------------+
| ConsecutiveNums |
+-----------------+
| 1               |
+-----------------+
Explanation: 1 is the only number that appears consecutively for at least three times.

Topics: Database

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Solutions

Solution 1: MS SQL (Best: 642 ms)

Metric	Value
Runtime	642 ms
Memory	N/A
Date	2018-04-14

Solution

/* Write your T-SQL query statement below */
SELECT DISTINCT A.Num AS ConsecutiveNums FROM
Logs A
LEFT JOIN Logs B on A.Id = B.Id-1
LEFT JOIN Logs C on A.Id = C.Id-2
WHERE A.Num = B.Num AND A.Num = C.Num

📜 1 more MS SQL submission(s)

Submission (2018-04-14) — 1391 ms, N/A

/* Write your T-SQL query statement below */
SELECT T.Num as ConsecutiveNums
FROM
(SELECT DISTINCT A.Num FROM
Logs A
LEFT JOIN Logs B on A.Id = B.Id-1
LEFT JOIN Logs C on A.Id = C.Id-2
WHERE A.Num = B.Num AND A.Num = C.Num) T

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Complexity Analysis

Approach	Time	Space
Solution	$O(n)$	$O(1) to O(n)$

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Interview Tips

Key Points

• Discuss the brute force approach first, then optimize. Explain your thought process.