冬令时个人打卡贴

Forgot to post yesterday

Day 32. Daily only. But I got my hardware and patent reading done

Day 33. Daily + high freq

845. Longest Mountain in Array

it is very clear that we only need to do one pass and just need to record if we are "climbing" or "going down" as well as record the max number

20. Valid Parentheses

Using stack

468. Validate IP Address

Be careful

39. Combination Sum

Cost me so long to find the correct way for backtracking. I think the diff btw DP and backtracking is that backtracking asks us to "just do it" and call self for next option.

22. Generate Parentheses

I am not sure if it will issue TLE when n is very large since I think there exists duplicate operations.

Day 34, Daily + high freq

Daily 858

Math

230

binary search tree + recursion

332

tree path: preorder+ inorder

105

I was doing it with backtracking idea. However, super slow.
I found one using multiset with stack that is decent and fast. But I am confused why such solution is working since I assume there exists backtracking?

417

I used to think it is like DP that fill all the cells.
However not. it is actually a DFS question.

Day 35 daily

Day 36. Daily. Need to work on a rebuttal

Day 37. Daily only.

82. Search in Rotate Sorted Array II

Find peak
Find the target

路过，高频题是不是绿色的就算高频?

Day 38

Day 39

Day 40

Day 41

Day 42 Daily + High Freq

Daily

keep finding until find one.
Since 11...11 = 11...1 * 10 + 1 so the mod result won't change when K is dividable by 2 or 5.

No.394 Decode String

Using stack. Like how we treat calculators

No.74 Search a 2D matrix

binary search x 2
I slightly change the mid in binary search so mid is a ceil result now

No.567 Permutation in string

sliding window. I think using constant vector will be way faster

No.127 Word Ladder

Mine is slow since I manually calculated the neighbours.
1) using * to save the effort for calculating neighbours
2) learn how to do a bidirectional way

No.442 Find all duplicates

Hash is the easiest way.
If we want to save space, we can use the item as the index, to do the "jump index" operation.
If it is jumped by other items, assign with -1
If it is a start item, assign with 0

fansian 发表于 2020-11-22 07:52
路过，高频题是不是绿色的就算高频?

Not really. Someone shared the high freq questions from various companies in the bbs. Guess it is summarized if you have LeetCode membership.