zhewuzhou/daily-challenges

This is the repository for solve algorithm problems

For now mainly focused on leetcode algorithms.

Problem solving techniques are well-known and buzz words most of the times.

For example: DP/Divide & Conquer, however for specific problems, it's normally very hard to get it right.

During the time of solve all those problems, I have found those tips really useful:

1. Play around the problem with some concrete examples, understand the problem deeply is key to solve it.

2. Write automation test for it, this is really useful for make more changes.

3. Whenever you find there are situations your solution missed, step back & and rethink if the direction is right.

4. Try best to reduce the problem into some well-know categories, it is normally pretty hard to implement an algorithm from ground.

Problem Category

Divide And Conquer

1. ReversePair493
2. CountOfRnage327
3. CountSmaller315

All of those challenges shares common stuff:

1. N^2 algorithm is exist and easy to do
2. NlgN algorithm are much harder
   • Stable sort with merge sort(NlgN)
   • Do count during the merge phase
   • It is always easier to separate the concerns by split the sort with count

TODOS

132 Recursion solution 126 DFS/BFS combined solution 174 Recursion solution