Advent of Code 2017 Day 2
Part 1
- A delightful treat of ease
- 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 eachchecksum
- 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()
andshift()
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
- Nested loops for the win
- 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
Animating my planned algorithm
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!
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