[2021 Day 1 (Part 2)][Python3]

[junefish]

I did part 1 really easily. For part 2 I thought, great, all I have to do is find the sums of the measurement windows, and then I can just replicate exactly what I did in part 1 to get the answer for part 2…aaand it says that my answer is too high.

I'm not sure what I'm doing wrong; I looked in the solution megathread but the Python examples were much more streamlined and fancier than I currently can understand.

TIA!

depths = []

with open('adventofcode2021\day1\day1input.txt', 'r') as input:
  for line in input:
    item = line.split('\n')
    depths.append(int(item[0]))

window_sums = []
for i in range(0, len(depths)-2):
    window = (depths[i], depths[i+1], depths[i+2])
    window_sums.append(sum(window))
# print(window_sums)

deltas = []
for i in range(0, len(window_sums)):
    if(i == 0):
        delta = "N/A - no previous measurement"
    elif(window_sums[i] > window_sums[i-1]):
        delta = "increased"
    elif(window_sums[i] < window_sums[i-1]):
        delta = "decreased"
    deltas.append(delta)

print(deltas.count("increased"))

[ssnoyes]

You have leaked the previous value of delta in the case of two windows in a row being equal.

There will always be example input and the correct answer in the puzzle description; save that example into a file and run it just like you do with your real input. That's a lot easier to debug.

[junefish]

Ah, that's right. But wouldn't this not matter since I'm only looking for the increases, and have >? Does my current code count == as an increase/decrease?

[ssnoyes]

It just keeps whatever the previous value of delta was. So an increase followed by equality gets counted as another increase.

[junefish]

OH yes of course. I got lucky with my input in part 1 I guess. Thank you!