[第二期活动] 在职刷题打卡，目标工作日一天2题，周末一天5题

Day 18
Take some time off to recover.
start w/ LC Explore, review 4 questions
3 longest substring w/ repeating character, two pointer + hashmap/array
11 contain with most water, two pointer
42 trapping rain water, two pointer (similar ^) or compare the diff between the min value of max left and right height at this point and the current bar (think each bar as an individual, array)
8 atoi, tedious case, need clarification

#Day_26

水两道，做道invert binary tree压压惊
Maximum Depth of Binary Tree
Invert Binary Tree

Day_15 (8/27)
Sliding puzzle II
Number of islands

打卡 Day 8
271. Encode and Decode Strings - Intuitive solution using non-ASCII character as delimiter.  A more versatile solution would be encoding length of each string and a regular delimiter.
168. Excel Sheet Column Title - There's no 0 in this number system. Therefore, when we hit 0, we need to borrow one carry from the number and make it "Z".
171. Excel Sheet Column Number - Easy
246. Strobogrammatic Number  
247. Strobogrammatic Number II - Backtracking
266. Palindrome Permutation - One pass O(n) using set

#Day_27

2题
Best Time to Buy and Sell Stock with Cooldown - local and global profit
Moving Average from Data Stream - 水

Revisited Best Time to Buy and Sell Stock I ~ III, 用DP解了I

day 25
Nested List Weight Sum
Flatten 2D Vector
Nested List Weight Sum II
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day 24
补昨天的，刷了没来更新。。。
Copy List with Random Pointer
Binary Tree Longest Consecutive Sequence II

Day_16 (8/28)

Valid Sudoku
Repeated DNA

#Day_28

Finished * 2
Sliding Window Maximum
Serialize and Deserialize BST

day 3 中间隔了两天 回加拿大
quick sort
reverse linkedlist recursive & iterative method
Remove Duplicates from a Linked List
Delete Node with a Given Key
Insertion Sort of a Linked List

Day 19
Trapping rain water II, pq

Day 20
compare version number, missing number, basic array
add two numbers I & II, basic linked list