Rising Temperature

LeetCode 197 | Difficulty: Easy

Easy

Problem Description

Table: Weather

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| recordDate    | date    |
| temperature   | int     |
+---------------+---------+
id is the column with unique values for this table.
There are no different rows with the same recordDate.
This table contains information about the temperature on a certain day.

Write a solution to find all dates' id with higher temperatures compared to its previous dates (yesterday).

Return the result table in any order.

The result format is in the following example.

Example 1:

Input: 
Weather table:
+----+------------+-------------+
| id | recordDate | temperature |
+----+------------+-------------+
| 1  | 2015-01-01 | 10          |
| 2  | 2015-01-02 | 25          |
| 3  | 2015-01-03 | 20          |
| 4  | 2015-01-04 | 30          |
+----+------------+-------------+
Output: 
+----+
| id |
+----+
| 2  |
| 4  |
+----+
Explanation: 
In 2015-01-02, the temperature was higher than the previous day (10 -> 25).
In 2015-01-04, the temperature was higher than the previous day (20 -> 30).

Topics: Database

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Approach

Direct Approach

This problem can typically be solved with straightforward iteration or simple data structure usage. Focus on correctness first, then optimize.

When to use

Basic problems that test fundamental programming skills.

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Solutions

Solution 1: MS SQL (Best: 779 ms)

Metric	Value
Runtime	779 ms
Memory	N/A
Date	2018-04-12

Solution

/* Write your T-SQL query statement below */
WITH CTE AS (
SELECT
rownum = ROW_NUMBER() OVER (ORDER BY w.RecordDate),
w.Id,
w.RecordDate,
w.Temperature
FROM Weather w
)
SELECT
CTE.Id
FROM CTE
LEFT JOIN CTE prev ON prev.rownum = CTE.rownum - 1
WHERE CTE.Temperature > prev.Temperature
AND DATEDIFF(DAY, prev.RecordDate, CTE.RecordDate) = 1

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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

• Start by clarifying edge cases: empty input, single element, all duplicates.