Ever since 2025, there has been an increasing number of in-depth problems involved in the seemingly resolvable coding interviews, which used to be very uncommon. It’s worthwhile noting that being unprepared for such topics but merely showing a problem-solving mindset may not always lead to a desirable passing-level result, given the extremely-competitive job market, while it’s also not recommended to learn by rote - memorizing the answer without thorough understanding could be easily recognized as imposter by the interviewers.

Discord Screen Challenge - Chat Server

Problem Statement

Original Problem Statement

Functional Requirements:

• The chat server should be capable of handling multiple clients connecting at the same time.
• Disconnection should be handled in a clean way.
• Should be able to receive and forward messages among clients (message is not echoed back to sender).

The questions below will be in a reverse-chronological order as they appeared in the interviews.

Simulated Calculator in String Processing

Calculator V1 - LC 224. Basic Calculator (Hard)

Essentially, merely +- arithmetic operations and parenthesis (nested possible) need to be supported.

Concise & efficient Solution after refactoring

Upon second thought, it appears that stack operations are need only when destructing parenthesis and processing the +- operators (see also other shared solutions on LeetCode).

Uber 60-min FE Interview - mid-July

Problem: on Hackerrank online IDE, given the function definitions, implement certain logic to obtain the expected output while ensuring the function calls running in parallel.

Note that (based on clarification made by the interviewer):

• Only JS/TS allowed for this problem;
• The function of getNameById is meant to simulate certain time consuming task; no change should be made other than under TODO inside asyncMap;
• callback param passed into getNameById is not the same as that in asyncMap.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

function getNameById(id, callback) {
  // simulating async request
  const randomRequestTime = Math.floor(Math.random() * 100) * 200;
  setTimeout(() => {
    callback("User" + id);
  }, randomRequestTime);
}

// Input
const userIds = [1, 2, 3, 4, 5];
async function asyncMap(input, iterateeFn, callback) {
  // TODO: implement this function, ensuring parallelism and the correct ordering in the output
}

asyncMap(userIds, getNameById, (names) => {
  console.log(names); // * ["user1", "user2", "user3", "user4", "user5"]
});

These usages are helpful to build a solution of NAS Status Monitor Visualization.

Fix pacman-mirrors: ModuleNotFoundError

Look for the missing modules failed to be imported:

1

sudo pacman -S python3 python-urllib3 python-charset-normalizer python-idna

Fix blocking pacman upgrade failure

Option 1:

1
2

sudo pacman-mirrors -g -f5
pamac upgrade --force-refresh

Option 2:

1

sudo pacman-mirrors --fasttrack && sudo pacman -Syyu

Also check for

1

yay -Suy

It’s sometimes possibly also needs to remove conflicting packages to proceed, rather than trying to install by force using the pacman options -d/-dd/-nodeps.

Allow installing dependencies from AUR

1

sudo pacman -S yay

UI tools

1
2
3

yay -S gotop
sudo pacman -S bspwm sxhkd polybar picom dunst dmenu nitrogen
sudo pacman -S mpd ncmpcpp

UI modules

1
2

sudo pacman -S rofi calc xorg xorg-xinit xorg-xbacklight alsa-utils
yay -S pywal networkmanager-dmenu

Font dependencies

1
2

sudo pacman -S ttf-font-awesome [ttf-dejavu]
yay -S ttf-material-design-iconic-font ttf-unifont ttf-cascadia-code ttf-nerd-fonts-symbols ttf-material-icons

Check if TTF fonts are present in the OS:

1
2

fc-cache -f -v
fc-list | grep ...

Clock

1

systemctl start mpd.service

Press = after starting ncmpcpp in CLI.

LRU Cache

1
2
3
4
5
6

class Node:
    def __init__(self, key, value):
        self.prev = None
        self.next = None
        self.key = key
        self.val = value

Dependencies

• Issue of dependency conflict or failure to find the dependency that should be there:

  sudo pacman -Syu –debug
  It triggers a prompt
  This also performs wide-range package upgrades.

• Issue of CMake / makepkg -si:

  1 2 3 4 5 6 7 8

  ==> Starting build()... CMake Error: CMake was unable to find a build program corresponding to "Unix Makefiles". CMAKE_MAKE_PROGRAM is not set. You probably need to select a different build tool. CMake Error: CMAKE_C_COMPILER not set, after EnableLanguage CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage -- Configuring incomplete, errors occurred! ==> ERROR: A failure occurred in build(). Aborting...

  To resolve such building depedencies:

  sudo pacman -S base-devel

  1 2 3 4 5

  Packages (12) autoconf-2.71-4 automake-1.16.5-2 bison-3.8.2-5 debugedit-5.0-5 flex-2.6.4-5 gc-8.2.2-1 guile-3.0.9-1 m4-1.4.19-3 make-4.4.1-2 patch-2.7.6-9 pkgconf-1.8.1-1 base-devel-1-2

• Install pytorch with ROCm backend (read more)

  For CPUs with AVX2 instruction set support, that is, CPU microarchitectures beyond Haswell (Intel, 2013) or Excavator (AMD, 2015), install python-pytorch-opt-rocm to benefit from performance optimizations. Otherwise install python-pytorch-rocm.

  sudo pacman -S python-pytorch-opt-rocm

  This may generate an installation as large as:

  1 2 3 4

  Total Download Size: 2654.00 MiB Total Installed Size: 29579.85 MiB :: Proceed with installation? [Y/n]

Appearance

• Icon font not displaying in Code terminal

  sudo pacman -S ttf-meslo-nerd-font-powerlevel10k

  1 2 3 4 5

  { ... "terminal.integrated.fontFamily": "MesloLGS NF", ... }

Preparation

A ZFS pool should surely pre-exist there to allow for the operations introduced later.

• Key point: Why not split, or shrink existing volumes for a Time Machine volume?

  Not viable. A ZFS partition always tries to occupy as much space as possible, so does ZFS volumes under it, sharing the entire space of it. To reserving some space is exactly what the quota property is designed for.

  In addition, you can use the reservation property to guarantee that a specified amount of disk space is available to a file system. Both properties apply to the dataset on which they are set and all descendents of that dataset.

  More…

• Creating a new ZFS filesystem

  zfs create -o compression=lz4 pool/filesystem

  where the purpose of an optional argument -o compression=lz4 is to turn on the compression for this dataset.

Unordered MultiSet

1
2
3
4
5
6
7
8
9
10
11
12
13

class MultiSet:
    def __init__(self):
        self.data = dict()
    
    def add(self, val):
        self.data[val] = 1 + (self.data[val] if val in self.data else 0)
    
    def remove(self, val):
        if not val in self.data:
            return
        self.data[val] -= 1
        if self.data[val] == 0:
            del self.data[val]

Fenwick Tree / Binary-indexed Tree

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

class BIT:
    def __init__(self, size):
        self.size = size
        self.data = [0] * size
    
    def add(self, pos, val):
        while pos < self.size:
            self.data[pos] += val
            pos += pos & (-pos)
    
    def query(self, pos):
        res = 0
        while pos > 0:
            res += self.data[pos]
            pos &= pos - 1
        return res

• Legacy Version

Number Theory

Quick power and modulo

To calculate $ n^m % mod $:

Division and modulo

DO NOT dividing an integer by another integer with respect to the modulus $mod$.
To calculate $ n/m%mod $ correctly ($ mod$ is a prime number thus $ φ(mod)=mod-1 $).
Use Eular function or modular multiplicative inversion.

Euler function $ φ(n) $

Quick greatest common divisor

1
2
3
4
5
6
7
8
9
10
11
12
13

def kgcd(a, b):
        if a == 0:
            return b
        if b == 0:
            return a
        if (a & 1) == 0 and (b & 1) == 0:
            return kgcd(a >> 1, b >> 1) << 1
        elif (b & 1) == 0:
            return kgcd(a, b >> 1)
        elif (a & 1) == 0:
            return kgcd(a >> 1, b)
        else:
            return kgcd(abs(a - b), min(a, b))

• Using Angular and Google API

• Two kinds of language API: GCP API and Chrome API.

• GCP API permission issue

• Authentication

• Sample TTS project

• Building a simple chrome extension

• THE BEGINNER’S GUIDE: Build a simple Chrome Extension in minutes