Robert Mion

Posted on

# Corruption Checksum

## Part 1

1. A delightful treat of ease
2. Animating my planned algorithm

### A delightful treat of ease

• A list of numbers
• Find the difference between the largest and smallest
• Sum up the absolute values of those differences

Sounds easy enough by now!

### Animating my planned algorithm

What I intend for my algorithm to do:

Time to build it!

### Writing my working algorithm

• A `reduce()` to tally up each `checksum`
• A regular expression to extract each row's numbers
• A `map()` to convert each matched string to a number
• A `sort()` to arrange numbers in ascending order
• `pop()` and `shift()` to subtract the first item from the last
``````return input
.split('\n')
.reduce((chucksums, row) => {
let cells = [...row.matchAll(/\d+/g)]
.map(match => +match[0])
.sort((a,b) => a - b)
return chucksums += cells.pop() - cells.shift()
}, 0)
``````

## Part 2

1. Nested loops for the win
2. Animating my planned algorithm

### Nested loops for the win

• After sorting each list, I will compare each value
• Worst case for my input, each line requires 16+15+14...+1 comparisons: that's under 150, times 16 lines: that's under 2200 total - no biggie

### Writing my working algorithm

``````return input
.split('\n')
.reduce((chucksums, row) => {
let cells = [...row.matchAll(/\d+/g)]
.map(match => +match[0])
.sort((a,b) => a - b)
let divisor = null
for (let i = 0; i < cells.length - 1; i++) {
for (let j = i + 1; j < cells.length; j++) {
if (
cells[j] / cells[i] ==
Math.round(cells[j] / cells[i])
) {
divisor = cells[j] / cells[i]
}
}
}
return chucksums += divisor
}, 0)
``````
• Unlike in the animation, my algorithm sorts in ascending order
• That's because it's more likely to run faster when starting with the smallest number, dividing by increasingly larger numbers

## I did it!!

• I solved both parts!
• I made a couple GIFs animating how my algorithms work!
• Both GIFs helped show me some errors and performance gains related to my algorithms!

Bring on Day 1!