[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

打卡Day 3

274. H-Index - Spent most of the time trying to figure out the definition..
169. Majority Element - Boyer-Moore Voting Algorithm, O(n) one pass
229. Majority Element II - Applying the same algorithm 2 times as there could be two candidates that appear more than [n/3] times
243. Shortest Word Distance
244. Shortest Word Distance II - Preprocessing the indices in a hash table
245. Shortest Word Distance III - Very similar to 243. Shortest Word Distance
217. Contains Duplicate  
219. Contains Duplicate II  
220. Contains Duplicate III - Bucket sort + sliding windows
188. Best Time to Buy and Sell Stock IV - bottom up dp - the use of local max and global max (hard)

Day_7 (8/19)

Factorization // deal when remain is 1
Sudoku Solver //  how to find the next empty spot in O(1)

#Day_6

692. top-k-frequent-words
6.zig-zag-conversion

xsijg8 发表于 2019-8-19 13:59
哇，一天八九题这个速度可以啊

谢谢鼓励 今天就有点偷懒了

打卡Day 4

376. Wiggle Subsequence - O(n) one pass greedy approach. Only peaks and valleys matter.
280. Wiggle Sort - O(n) one pass. Could get rid of the sign variable by noticing if the index is odd/even.
324. Wiggle Sort II - Easy if sorting is allowed. Hard using quickSelect to first select the medium of the array (deterministic selection is even better), and then place larger numbers on odd indices, smaller numbers on even indices. A lot of work - implementation wise.
113. Path Sum II - DFS

#Day_19

Finished * 2
Spiral Matrix II
Evaluate Reverse Polish Notation

day 16
Minimum Depth of Binary Tree
Maximum Depth of Binary Tree
Balanced Binary Tree

Day 15
Revisit how to do tree traversal iteratively
98 validate binary search tree, recursively or iteratively with prev
173 binary search tree iterator, either inorder array, or inorder stack iterative
199 binary tree right side view + 958 check completeness of a binary tree, bfs
501 find mode in binary search tree, brute force recursively w/ hash, or use stack iteratively to do two pass
257 binary tree path, dfs, be careful with backtracking and definition of leaf

day 17
Recover Binary Search Tree
Verify Preorder Sequence in Binary Search Tree
这两题都没啥清晰思路，看了答案然后自己想了一遍写了。

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昨天写好了忘记点发送，今天补打卡= =

Day_8 (8/20)

Expression Add Operations
Generalized Abbreviation
// In DFS, try to avoid for-loop which may cause MLE and duplicate items