Hard

Pending
56 Merge Intervals
146 LRU Cache
158 Read N Characters Given Read4 II - Call multiple times

Done
33 Search in Rotated Sorted Array (Array_Hard)
117 Populating Next Right Pointers in Each Node II (Tree_Hard)
287 Find the Duplicate Number(Array_Hard, binary-search!)
297 Serialize and Deserialize Binary Tree (Tree_Hard)