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LeetCode SQL 50 Solution/180. Consecutive Numbers/readme.md

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+# 180. Consecutive Numbers
+
+## Problem Statement
+You are given a table `Logs` with the following structure:
+
+```
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| id          | int     |
+| num         | varchar |
++-------------+---------+
+```
+- `id` is the primary key and auto-increments starting from 1.
+- Find all numbers that appear **at least three times consecutively**.
+- Return the result table in **any order**.
+
+## Example 1:
+
+**Input:**
+
+```
+Logs table:
++----+-----+
+| id | num |
++----+-----+
+| 1  | 1   |
+| 2  | 1   |
+| 3  | 1   |
+| 4  | 2   |
+| 5  | 1   |
+| 6  | 2   |
+| 7  | 2   |
++----+-----+
+```
+
+**Output:**
+
+```
++-----------------+
+| ConsecutiveNums |
++-----------------+
+| 1               |
++-----------------+
+```
+
+---
+
+## Solution Approaches
+
+### **SQL Solution (Using Self Join)**
+```sql
+SELECT DISTINCT l1.num AS ConsecutiveNums
+FROM Logs l1
+JOIN Logs l2 ON l1.id = l2.id - 1 AND l1.num = l2.num
+JOIN Logs l3 ON l1.id = l3.id - 2 AND l1.num = l3.num;
+```
+
+### **SQL Solution (Using Window Functions)**
+```sql
+SELECT DISTINCT num AS ConsecutiveNums
+FROM (
+    SELECT num, LAG(num,1) OVER (ORDER BY id) AS prev1,
+                LAG(num,2) OVER (ORDER BY id) AS prev2
+    FROM Logs
+) temp
+WHERE num = prev1 AND num = prev2;
+```
+
+### **Pandas Solution**
+```python
+import pandas as pd
+
+def consecutive_numbers(logs: pd.DataFrame) -> pd.DataFrame:
+    logs['prev1'] = logs['num'].shift(1)
+    logs['prev2'] = logs['num'].shift(2)
+
+    result = logs[(logs['num'] == logs['prev1']) & (logs['num'] == logs['prev2'])]
+    return pd.DataFrame({'ConsecutiveNums': result['num'].unique()})
+```
+
+---
+
+
+## File Structure
+```
+📂 Problem Name
+ ├── 📄 README.md       # Problem statement, approach, solution
+ ├── 📄 sql_solution.sql  # SQL Solution
+ ├── 📄 pandas_solution.py   # Pandas Solution
+ └── 📄 example_input_output.txt  # Sample input & expected output
+```
+
+## Useful Links
+- [LeetCode Problem](https://leetcode.com/problems/consecutive-numbers/) 🚀
+- [SQL `JOIN` Explained](https://www.w3schools.com/sql/sql_join.asp)
+- [MySQL `LAG()` Window Function](https://dev.mysql.com/doc/refman/8.0/en/window-function-descriptions.html)
+
+---
+
+Feel free to contribute with optimized solutions! 💡