added hash set and valid sudoku solutions

Author: mihirs16

03. Data Structures/Hash Tables/Hash_Set.py

@@ -0,0 +1,57 @@
+# hashset | leetcode 705 | https://leetcode.com/problems/design-hashset/
+class HashSet:
+
+    # constructor
+    def __init__ (self, hash_set = None):
+        '''initialize a hash set'''
+        self.hash_set: dict = {} if hash_set == None else hash_set
+        self.size: int = len(self.hash_set.keys())
+
+    # initialize iterator for __iter__
+    def __iter__ (self):
+        self.n = 0
+        return self
+    
+    # return next element for __next__
+    def __next__ (self):
+        if self.n < self.size:
+            result = list(self.hash_set.keys())[self.n]
+            self.n = self.n + 1
+            return result
+        else:
+            raise StopIteration
+
+    def add (self, key) -> None:
+        '''add element to hash set'''
+        self.hash_set[key] = True
+        self.size = self.size + 1
+
+    def contains (self, key) -> bool:
+        '''does hash set contain element'''
+        return True if self.hash_set.get(key) else False
+
+    def remove (self, key) -> None:
+        '''remove element from hash set'''
+        if self.contains(key):
+            self.hash_set.pop(key)
+            self.size = self.size - 1
+
+# initialize a new hashset
+hashSet = HashSet()
+
+# add values to a hash set
+hashSet.add('first')
+hashSet.add('second')
+hashSet.add('third')
+hashSet.add('fourth')
+
+# remove from a hash set
+hashSet.remove('fourth')
+
+# check if value exists in a hash set
+print(hashSet.contains('first'))
+print(hashSet.contains('fourth'))
+
+# iterate through a hash set
+for element in hashSet:
+    print(element)

03. Data Structures/Hash Tables/Valid_Sudoku.py

@@ -0,0 +1,30 @@
+# valid sudoku | leetcode 36 | https://leetcode.com/problems/valid-sudoku/
+# Determine if a n^2 x n^2 Psuedo-Sudoku board is valid. 
+# Only the filled cells need to be validated.
+
+import collections
+
+class Solution:
+    def isValidSudoku(self, board: list[list[str]]) -> bool:
+        rows = collections.defaultdict(set)
+        columns = collections.defaultdict(set)
+        squares = collections.defaultdict(set)
+        
+        for i in range(len(board)):
+            for j in range(len(board[i])):
+                
+                if board[i][j] == '.':
+                    continue
+                
+                isInRow = board[i][j] in rows[i]
+                isInColumn = board[i][j] in columns[j]
+                isInSquare = board[i][j] in squares[(i//3, j//3)]
+                if (isInRow or isInColumn or isInSquare):
+                    return False
+                
+                rows[i].add(board[i][j])
+                columns[j].add(board[i][j])
+                squares[(i//3, j//3)].add(board[i][j])
+        
+        return True                
+            

readme.md

@@ -1,15 +1,16 @@
 # Data Structures and Algorithms
 
-![](https://img.shields.io/github/issues/shushrutsharma/Data-Structures-and-Algorithms-Python?color=red&style=for-the-badge)
-![](https://img.shields.io/github/issues-pr-closed/shushrutsharma/Data-Structures-and-Algorithms-Python?style=for-the-badge)
-![](https://img.shields.io/github/stars/shushrutsharma/Data-Structures-and-Algorithms-Python?style=for-the-badge)
-![](https://img.shields.io/badge/Built%20With-Python-blueviolet?style=for-the-badge)
+![Issues](https://img.shields.io/github/issues/shushrutsharma/Data-Structures-and-Algorithms-Python?color=red&style=for-the-badge)
+![PRs](https://img.shields.io/github/issues-pr-closed/shushrutsharma/Data-Structures-and-Algorithms-Python?style=for-the-badge)
+![Stars](https://img.shields.io/github/stars/shushrutsharma/Data-Structures-and-Algorithms-Python?style=for-the-badge)
+![Built With](https://img.shields.io/badge/Built%20With-Python-blueviolet?style=for-the-badge)
 
 All the essential resources and template code needed to understand and practice data structures and algorithms in python with few small projects to demonstrate their practical application.
 
 ## Index
 
 ### 1. 📚 [Resources](/01.%20Resources/)
+
 1. [Books](/01.%20Resources/Books/)
     - [Data Structures - Reema Thareja](/01.%20Resources/Books/Data%20Structures%20-%20Reema%20Thareja.pdf)
     - [competitiveCoding](https://github.com/mihirs16/Data-Structures-and-Algorithms-Python/blob/master/01.%20Resources/Books/competitiveCoding.pdf)
@@ -20,12 +21,14 @@ All the essential resources and template code needed to understand and practice
 6. [Master the Interview](/01.%20Resources/Master_the_Interview.pdf)
 
 ### 2. ⭕ [Big-O](/02.%20Big-O/)
+
 1. [O(1)](/02.%20Big-O/O(1).py)
 2. [O(m+n)](/02.%20Big-O/O(m%20+%20n).py)
 3. [O(n)](/02.%20Big-O/O(m%20x%20n).py)
 4. [O(n^2)](/02.%20Big-O/O(n^2).py)
 
 ### 3. 🏢 [Data Structures](/03.%20Data%20Structures/)
+
 1. [Arrays](/03.%20Data%20Structures/Arrays/)
 2. [Graphs](/03.%20Data%20Structures/Graphs)
 3. [Hash Tables (Dictionary)](/03.%20Data%20Structures/Hash%20Tables)
@@ -35,20 +38,22 @@ All the essential resources and template code needed to understand and practice
 7. [Trees](/03.%20Data%20Structures/Trees)
 
 ### 4. 🛠 [Algorithms](/04.%20Algorithms/)
+
 1. [Divide and Conquer](/04.%20Algorithms/Divide%20and%20Conquer/)
 2. [Dynamic Programming](/04.%20Algorithms/Dynamic%20Programming/)
 3. [Recursion](/04.%20Algorithms/Recursion/)
 4. [Sorting](/04.%20Algorithms/Sorting/)
 5. [Traversals](/04.%20Algorithms/Traversals)
 
 ### 5. 📂 [File Handling and OOPS](/05.%20File%20Handling%20and%20OOPS/)
+
 1. [File + Classes Demo](/05.%20File%20Handling%20and%20OOPS/file%2Bclasses.py)
 
-# Additional: 
+## Additional
 
 ### 6. ❗ [Error Handling](/06.%20Error%20Handling/)
 
-### 7. ➗ [Functional Programming](/07.%20Functional%20Programming/) 
+### 7. ➗ [Functional Programming](/07.%20Functional%20Programming/)
 
 ### 8. 🎉 [Decorators](/08.%20Decorators/)
 
@@ -60,9 +65,8 @@ All the essential resources and template code needed to understand and practice
 
 ### 12. 🧪 [Unit Testing](/12.%20Unit%20Testing/)
 
-------------------------------------------
-
 ### 13. 👷 ‍[Projects](/13.%20Mini-Projects/)
+
 1. [Job Scheduler](/13.%20Mini-Projects/Job%20Scheduler)
 2. [Email Project](/13.%20Mini-Projects/email_project)
 3. [Hash Project](/13.%20Mini-Projects/hash_project)