🚀 7. How do you handle collisions in a hash table?
A collision happens when two keys generate the same index.

🔹 Example:
hash("abc") = 5
hash("xyz") = 5
Both want index 5.

🔹 Collision Handling Techniques

1️⃣ Chaining
Store multiple values in a linked list.
Index 5: abc → xyz

2️⃣ Open Addressing
Find another empty slot.
Methods: Linear probing, Quadratic probing, Double hashing

🔹 Linear Probing Example
Index occupied? Move to next slot.

🔹 Interview Tip
Most interviewers expect Chaining and Linear probing to be explained clearly.

🚀 8. What is a binary tree and a binary search tree (BST)?

🔹 Binary Tree
A tree where each node has at most 2 children.
10
/ \
5 20

🔹 Binary Search Tree (BST)
Special binary tree where: Left < Root < Right
10
/ \
5 20

🔹 BST Advantages
Fast searching, Sorted traversal, Efficient insert/delete

🔹 Complexity
Operation | Average
Search | O(log n)
Insert | O(log n)
Delete | O(log n)

Worst case: O(n)

🔹 Interview Tip
BST questions are among the most asked DSA interview topics.

🚀 9. How do you traverse a tree (inorder, preorder, postorder)?
Tree traversal means visiting all nodes.

🔹 Inorder Traversal
Left → Root → Right
def inorder(root):
if root:
inorder(root.left)
print(root.val)
inorder(root.right)

➡️ Used in BST to get sorted order.

🔹 Preorder Traversal
Root → Left → Right
Used for: Tree copying, Serialization

🔹 Postorder Traversal
Left → Right → Root
Used for: Deletion, Bottom-up processing

🔹 Complexity
All traversals: Time O(n), Space O(h)

🚀 10. What is recursion and when is it useful?
Recursion is when a function calls itself.

🔹 Example:
def factorial(n):
if n == 0:
return 1
return n * factorial(n - 1)

🔹 Recursive Flow
factorial(4) = 4 × factorial(3) = 4 × 3 × factorial(2)...

🔹 Key Components
1. Base case
2. Recursive case

🔹 Where Recursion is Useful
Trees, Graphs, DFS, Backtracking, Divide & Conquer

🔹 Interview Tip
Always explain: Base condition, Stack usage, Time complexity

🔹 Common Mistake
Missing base case causes: Stack Overflow Error

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