YoungForest's blog

This was my first biweekly contest after returning to China. My hands were a bit rusty, and my form was still recovering. Recently, because of the novel coronavirus epidemic, I have been isolating at home and almost cannot go out except to buy groceries. The New Year atmosphere disappeared this year because of it. Staying at home almost made me go stir-crazy. The contest result was okay. Speed contests have also always been a type I am not good at.

1342. Number of Steps to Reduce a Number to Zero

This week my glasses broke, so I was not in form. Dinner at home was also late, so I did not finish the problems.

1346. Check If N and Its Double Exist

I finally returned to my dear motherland. I can get up on Sunday morning to play LeetCode contests again. I have to admit that after four months away, I became much rustier. The ranking says it all.
This contest was purely a speed contest, and speed depends heavily on form and familiarity. So I fully accept the drop in ranking. It also happens to push me to put more effort into preparing for the upcoming Google interview.

1341. The K Weakest Rows in a Matrix

This started from a LeetCode problem: 1286. Iterator for Combination. The most perfect implementation would use a Generator, namely Python’s yield. But I did not know how to do that, so I only implemented a solution that precomputes everything and stores the results. It was not elegant. After the contest, I learned an implementation of Generator in C++ and am sharing it here. I did not find a good Chinese article about this online.

The root of the problem is that a classmate asked about a lucky number problem: Codeforces 280B. Codeforces 281D is the same problem.

Find all unique pairs of maximum and second maximum elements over all sub-arrays in O(NlogN)

A lucky number is defined as the XOR value of the maximum and second maximum of a subarray. The task is to find the largest lucky number among all lucky numbers.

I did not go out this week, and happened to run into the biweekly contest. It had been a long time since I joined one, so it really felt rare.
All the problems in this biweekly contest were standard and not hard. I finished everything with one AC on each problem and still had 50 minutes left. A typical speed contest.

Before the contest ended, my rank was 92, with 1900 participants. After the contest, I found that my rank had dropped. I guessed, and then verified, that the post-contest ranking included users from the China region. The increase in the number of participants and the change in first place matched my guess exactly. I checked leetcode-cn, where the ranking is split into China region and global region. Looks like I need to work even harder in future contests; many people I do not know are competing in the same contests from the China region.

A practical guide to choosing, opening, and using bank accounts while living in Europe.

Because Europe was on winter time, I was in UTC +1.00, so for this contest I deliberately got up at 6 a.m. to participate. After finishing, I rested for an hour, then went to Ghent with friends for the whole day. When I came back at night, I suddenly remembered that Machine Learning assignment 2 was due that day, and then started rushing the deadline like crazy. Facts proved that without studying seriously, I still could not handle the assignment. I submitted something rough; better than not submitting at all. For the blank questions, I generously told the TA that I simply did not know how to do them.

This was the last round of Kick Start 2019, and I still really wanted to participate. This year I participated in six Kick Start rounds in total. Although I already got an interview invitation in Round A, I still could not afford to be careless. The rankings for each round are shown below:

Using macOS does have some inconvenient parts, such as writing to NTFS hard drives or USB drives. By default, Mac only supports reading NTFS. But as long as you have the courage to tinker, the solution is still very simple.

Most Recommended Method

Mounty for NTFS

1232. Check If It Is a Straight Line

Check whether every three consecutive points are collinear.

Time complexity: O(N),
space complexity: O(1).