[第三期活动] 在职刷题打卡，目标工作日一天2题，周末一天5题

# Day 5

* Adding Two Negabinary Numbers
* Super Pow

day 18
mock interview了一题
新写了一题没写过- =，其实是两边往中间夹，然后填dp的顺序比较特殊。
Longest Palindromic Subsequence
复习了一题，之前自己写出来的，这次愣是看了好久：
Regular Expression Matching

Day 8, array focus
1. intersection of two arrays, follow up more in data processing direction, what if one array could not be processed in memory
  - hash table
  - sort + two pointer
  => find common characters, hash table
2. matrix multiplication, math
3. range sum query 2d, similar to prefix sum, make sure you draw it out and have a solid math function
4. trapping rain water, two pointer
5. longest substring without repeating character, sliding window + hash map
6. product of array except self, two pass, from left & right
7. diagonal traverse, know that when (col + row).even?, direction is always going up
8. maximum swap, bucket sort?
9. longest continuous increasing subsequence, easy..

09/22
303. Range Sum Query - Immutable
307. Range Sum Query - Mutable
308. Range Sum Query 2D - Mutable
304. Range Sum Query 2D - Immutable

# Day_22
Array
Sort Colors
Move Zeroes

Day_21 (9/21)

Subtree of another tree
Merge two sorted lists
Symmetric tree
First unique character in a string
Second minimum node in a binary tree

#Day_13

1200. Minimum Absolute
1202. Smallest String with Swaps

Was busy with work...sigh..

Day 7, sort focus
21 & 23, merge list, for 23, heap or divide & conquer
252, sort, then check overlap.
253, this is a really interesting problem to think through
  1. The start time of the meeting indicates a room is occupied, while the end time of the meeting indicates a room is available. This breaks the concept of meeting interval and focuses at the meeting room (the resources).
      Iterate through all the sorted timestamps, if it is a start time, add to the queue. If it is an end time, pop the queue.
      Record the max length of the queue, which will be the most meeting rooms needed.
  2. Use heap to store "all conflicting events". Refer this for details, https://leetcode.com/problems/me ... ion-using-min-heap. And this will be great solution to answer the followup like, print the meeting list in all the meeting rooms.
791, hashmap, then re-assemble the string
215, 347, 973 top k revisit, 1. sort 2. heap(ds) 3. quick select

Day 5
965. Univalued Binary Tree
236. Lowest Common Ancestor of a Binary Tree

Stage II : 分类各个击破
day16-09/22-DP&sort的一天，初级DP还好，稍微复杂一点果然搞定不了，有集体明明做过了的还是没能做出来，stage2完了以后要开始每天review没有做出来的题，需要借助记忆曲线了, 24 in total
binary search:
1. 300. Longest Increasing Subsequence
sort:
1. 280. Wiggle Sort
2. 41. First Missing Positive
3. 179. Largest Number
4. 56. Merge Intervals
5. 57. Insert Interval
6. 253. Meeting Rooms II
7. 252. Meeting Rooms
8. 296. Best Meeting Point
9. 164. Maximum Gap
10. 147. Insertion Sort List
11. 148. Sort List
12. 75. Sort Colors
DP:
1. 139. Word Break
2. 132. Palindrome Partitioning II
3. 647. Palindromic Substrings
4. 45. Jump Game II
5. 122. Best Time to Buy and Sell Stock II
6. 121. Best Time to Buy and Sell Stock
7. 152. Maximum Product Subarray
8. 53. Maximum Subarray
9. 96. Unique Binary Search Trees
10. 91. Decode Ways
11. 70. Climbing Stairs