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November 15th, 2024

Bouncing balls, again (IV)

Euler problem 14

Today’s problem was to find the longest chain and my solution looks like this:

function main() {
  let biggestLength = 0;
  let biggestValue = 0;
 
  for (let i = 1; i < 1_000_000; i++) {
    const chain = takeAll(collatz(i));
 
    if (chain.length > biggestLength) {
      biggestLength = chain.length;
      biggestValue = i
    }
  }
 
  console.log(biggestValue, biggestLength)
}

This isn’t exactly what I want to write. I want to write something closer to this:

const a = range(1, 1_000_000)
  .map(collatz)
  .map(takeAll)
  .sort(longestToShortest)[0][0]

But if I do this my poor laptop runs out of memory and Javascript exits and I don’t get an answer. can see why- this asks the machine to keep everything in memory. I think maybe a way around this is a generator that returns the biggest length seen so far. I can’t quite see the solution to that, though, because I need to control the value feeding into the generator (the n that collatz is starting at) and the output (the length of the array).

Missing Semester Homework 2

Question 1

Read man ls and write an ls command that lists files in the following manner

  • Includes all files, including hidden files
euler/014 main 
❯ ls -a
.  ..  main.ts
  • Sizes are listed in human readable format (e.g. 454M instead of 454279954)
❯ ls -lh
total 672M
-rw-r--r-- 1 nicole nicole 145M Feb 18  2020 'Broot： An Innovative Way To View Your Linux File System [eTtarjSJ0yU].mp4'
-rw-r--r-- 1 nicole nicole 105M Feb  3  2020 'Broot Is A Better Way To Navigate Directories [lGD-wsQO_lI].mp4'
-rw-r--r-- 1 nicole nicole  74M Aug 27 16:20 'I'\''M GOING TO USE THE NNN FILE BROWSER! 😮 [U2n5aGqou9E].mp4'
-rw-r--r-- 1 nicole nicole 252M Nov 17  2020 'NNN file manager and plugin system (revisited) [-knZwdd1ScU].mp4'
-rw-r--r-- 1 nicole nicole  98M Aug 28 03:02 'nnn file manager basics - Linux [il2Fm-KJJfM].mp4'
  • Files are ordered by recency
❯ ls -alt
total 687700
drwx------ 39 nicole nicole      4096 Nov 15 13:36  ..
drwxr-xr-x  2 nicole nicole      4096 Nov 14 19:58  .
-rw-r--r--  1 nicole nicole 102596284 Aug 28 03:02 'nnn file manager basics - Linux [il2Fm-KJJfM].mp4'
-rw-r--r--  1 nicole nicole  76583213 Aug 27 16:20 'I'\''M GOING TO USE THE NNN FILE BROWSER! 😮 [U2n5aGqou9E].mp4'
-rw-r--r--  1 nicole nicole 264003848 Nov 17  2020 'NNN file manager and plugin system (revisited) [-knZwdd1ScU].mp4'
-rw-r--r--  1 nicole nicole 151358168 Feb 18  2020 'Broot： An Innovative Way To View Your Linux File System [eTtarjSJ0yU].mp4'
-rw-r--r--  1 nicole nicole 109641797 Feb  3  2020 'Broot Is A Better Way To Navigate Directories [lGD-wsQO_lI].mp4'

Output is colorized

❯ ls --color
Applications  Arduino  battery.sh  coding-math  dead.letter  Desktop  Documents  Downloads  Music  Pictures  Public  Templates  Videos  workspace

Question 2

Write bash functions marco and polo that do the following. Whenever you execute marco the current working directory should be saved in some manner, then when you execute polo, no matter what directory you are in, polo should cd you back to the directory where you executed marco. For ease of debugging you can write the code in a file marco.sh and (re)load the definitions to your shell by executing source marco.sh.

Marco:

#! /usr/bin/env bash
 
echo $(pwd) >~/.marco-save

Polo:

#! /usr/bin/env bash
 
file=~/.marco-save
if [ ! -e "$file" ]; then
    echo "Run marco first!"
    exit 1
fi
 
cd $(cat ~/.marco-save)

Question 3

Say you have a command that fails rarely. In order to debug it you need to capture its output but it can be time consuming to get a failure run. Write a bash script that runs the following script until it fails and captures its standard output and error streams to files and prints everything at the end. Bonus points if you can also report how many runs it took for the script to fail.

#! /usr/bin/env bash
 
if [ "$#" -ne 1 ]; then
    echo "Pass the program to run"
fi
 
COUNTER=1
while true; do
    CODE=$(bash "$1")
 
    if [ "$?" -ne 0 ]; then
        echo "Took $COUNTER runs"
        exit 0
    fi
 
    COUNTER=$((COUNTER + 1))
done
#! /usr/bin/env bash
 
if [ "$#" -ne 1 ]; then
    echo "Pass the program to run"
fi
 
COUNTER=1
while true; do
    CODE=$(bash "$1")
 
    if [ "$?" -ne 0 ]; then
        echo "Took $COUNTER runs"
        exit 0
    fi
 
    COUNTER=$((COUNTER + 1))
done

Question 4

As we covered in the lecture find’s -exec can be very powerful for performing operations over the files we are searching for. However, what if we want to do something with all the files, like creating a zip file? As you have seen so far commands will take input from both arguments and STDIN. When piping commands, we are connecting STDOUT to STDIN, but some commands like tar take inputs from arguments. To bridge this disconnect there’s the xargs command which will execute a command using STDIN as arguments. For example ls | xargs rm will delete the files in the current directory.

Your task is to write a command that recursively finds all HTML files in the folder and makes a zip with them. Note that your command should work even if the files have spaces (hint: check -d flag for xargs).

If you’re on macOS, note that the default BSD find is different from the one included in GNU coreutils. You can use -print0 on find and the -0 flag on xargs. As a macOS user, you should be aware that command-line utilities shipped with macOS may differ from the GNU counterparts; you can install the GNU versions if you like by using brew.

find -name "*.html" -print0 | xargs -0 -P 4 -n 1 gzip

End of day

Today was a great day! I had a chance to share, be social, and do some work on things I’m interested in.

Worked on Today

Tomorrow

This weekend I need to rest. I think I’m going to pick on the days and intentionally not program (or do less). I’ve had 2 nights since I’ve been at RC where I’ve needed 10+ hours of sleep and I think a little break might help make me more effective heading into next week.