1. Two Sum (Array, Hash Table)
Problem: Given an array of integers nums and an integer target, return indices of the two numbers that add up to target.
2. Valid Parentheses (Stack)
Problem: Check if a string containing '(', ')', '{', '}', '[', ']' is valid.
3. Merge Two Sorted Lists (Linked List)
Problem: Merge two sorted linked lists into one sorted list.
4. Maximum Subarray (Dynamic Programming)
Problem: Find the contiguous subarray with the largest sum (Kadane's Algorithm).
5. Binary Tree Level Order Traversal (BFS)
Problem: Return the level order traversal of a binary tree.
6. Longest Substring Without Repeating Characters (Sliding Window)
Problem: Find the length of the longest substring without repeating characters.
7. LRU Cache (Design)
Problem: Design an LRU (Least Recently Used) cache.
8. Merge Intervals (Sorting)
Problem: Merge overlapping intervals.
9. Word Break (DP)
Problem: Check if a string can be segmented into dictionary words.
10. Clone Graph (DFS/BFS)
Problem: Clone an undirected graph.
11. Top K Frequent Elements (Heap)
Problem: Return the top k frequent elements.
