• MergeSort
• QuickSort
• BubbleSort

• Hashmap
• Stack
• Queue
• DoubleEndedQueue Deque
• Linked list
  • Reverse a linked list
  • Merge two sorted list
  • Palindrome linked list
• Trees (n-ary, trie, heap)
  • Quad Tree
  • Inorder, pre, post order traversal
  • Maximum depth of a binary tree
  • Validate Binary search Tree
  • Convert sorted array to binary search tree

- Abstraction 
- Inheritance 
- Cohesion 
- Coupling

- Maps
- Lists
- Concurrency

- BFS 
- DFS 
- Shortest path algorithm like Dijkstra's

- Working with bit maps 
- Bit shifting

- Reverse a number
- Pow (x,n)
- Fibonacci
- Merge 2 sorted lists
- Reverse linked list
- Search in a binary tree
- Time complexity & space complexity analysis

- Singleton
- Factory
- Fasade

- Best time to buy a stock
- Fibonacci series
- Longest palindromic substring
- 

Here are some reference materials for you: ▪ LeetCode.com ▪ Hackerrank.com

For Problem Solving some channels: • https://www.youtube.com/c/CSDojo • https://www.youtube.com/channel/UC1fLEeYICmo3O9cUsqIi7HA • https://www.youtube.com/channel/UCKvwPt6BifPP54yzH99ff1g • https://www.youtube.com/channel/UCmJz2DV1a3yfgrR7GqRtUUA • https://www.youtube.com/channel/UCMn3_305DqmTylxJPFA8OJA (This guy I like really)

For System Design : • https://www.youtube.com/user/tusharroy2525 (Very Good) • https://www.youtube.com/channel/UCRPMAqdtSgd0Ipeef7iFsKw (very good) • https://www.youtube.com/watch?v=ZgdS0EUmn70&list=PL73KFetZlkJSZ9vTDSJ1swZhe6CIYkqTL (This is list of videos) • https://www.youtube.com/watch?v=siqiJAJWUVg&list=PLK8IOvtbwVsuYW8KovGg9o6dlhspym8O_ ((Nice guy with decent videos on design) • https://www.educative.io/courses/grokking-the-system-design-interview

Leetcode has contests, mock interviews, company specific problems, top questions being asked and much else. This is definitely worth the money.