Others
Here are some other questions that do not fit in other categories.
We recommend: Trapping Rain Water and The Skyline Problem.
If you'd like more challenge, we highly recommend you to solve the last two problems: The Skyline Problem and Largest Rectangle in Histogram. Both problems are very fun to solve and can be solved with many different approaches.
Queue Reconstruction by Height
Trapping Rain Water
The Skyline Problem
Largest Rectangle in Histogram
leetcode.com/problems/queue-reconstruction-by-height/solution/
leetcode.com/problems/trapping-rain-water/solution/
leetcode.com/problems/the-skyline-problem/solution/
leetcode.com/problems/largest-rectangle-in-histogram/solution/