On 2018 Christmas I posted an article upon finishing all easy-level problems of LeetCode. I said I will keep solving medium level ones. I did, and today I solved 100 out of 496 (as of this writing; LeetCode hosts weekly contest and add the problems to the list afterwards). It's been about 73 days since 2018/12/25 in which I have solved 24, but I was away on vacation, and I spent late December + early January mostly on becoming Certified Solidworks Expert, so I solved additional 76 problems in about a month and a week. Two problems per day on the average.
I solved medium level problems in descending order of acceptance. Meaning that I started from the easiest problems to progressively harder ones. But medium was medium. Significantly more difficult than easy ones. Easy problems were mostly about the basics; straightforward questions with good understanding of key data structure & algorithm. Medium problems went one step further in, demanding application (not too hard though) of basic concepts. One has to think quite a bit to decipher the required logic, implementation is more complicated and prone to mistake, and the final codes are longer. Moreover, there are algorithm topics of commensurate difficulty such as dynamic programming / Disjoint set & union find / Bitwise manipulation / stack / etc. I had to learn and review them carefully, so I couldn't solve 10 problems a day like I did with easy ones. However, the harder the problems are, the greater the thrills of solving them. That is the ultimate, undeniable attraction intellectually challenging questions in math / physics / coding have to offer.
I keep most of the source codes I wrote and associated thought process in my Gmail account for convenient re-visiting in the future. So far I am the more and more fascinated by these coding problems. Will keep it up!
