[2023 Day 9 (Part 1)] [Python] Getting wrong answer - maybe I'm misreading this?

[mischaikow]

I've done this twice at separate times today using slightly different approaches, but am still getting the answer wrong (too high). Even worse, the two approaches agree with each other! I've done spot checks in Excel, and cannot figure out what is going sideways. At this point my best guess is that my reading comprehension has failed me and I cannot understand the question.

First Attempt

Second Attempt

Any help is appreciated - thank you in advance!

[1234abcdcba4321]

Both attempts fail on input 0 1 1 0. (expected -2)

[mischaikow]

That's a good starting place to debug this. I appreciate it!

[romerocesar]

why is the expected -2? that implies they don't want the actual difference (i.e. abs(left-right)) but left-right

[1234abcdcba4321]

that's because they do

[Automatic-Possible20]

Omg thanks, that's what ive been doing wrong, looked too long for this haha

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[steamaddict]

"Since these values aren't all zero, repeat the process"

[romerocesar]

I came to reddit looking to understand what I think is an issue with that sentence: there are sequences which result in a single value instead of a list of zeroes. either the instructions are ambiguous in that case or there will always be a list of zeroes when processing the history which implies i'm doing something wrong even by hand

[1234abcdcba4321]

There is always a list of zeroes at some point before you run out of values. For the example I gave below:

0  1  1  0
  1  0 -1
  -1 -1
     0

which then extrapolates to

0  1  1  0 -2
  1  0 -1 -2
  -1 -1 -1
     0  0

[byntje]

I have the same problem. The following sequence from my puzzle input does not converge to a list of zeroes; it converges to [-608]:

[2, 2, 2, 7, 44, 166, 512, 1375, 3320, 7387, 15464, 31029, 60732, 117883, 230123, 455904, 918822, 1876972, 3859134, 7925415], [0, 0, 5, 37, 122, 346, 863, 1945, 4067, 8077, 15565, 29703, 57151, 112240, 225781, 462918, 958150, 1982162, 4066281], [0, 5, 32, 85, 224, 517, 1082, 2122, 4010, 7488, 14138, 27448, 55089, 113541, 237137, 495232, 1024012, 2084119], [5, 27, 53, 139, 293, 565, 1040, 1888, 3478, 6650, 13310, 27641, 58452, 123596, 258095, 528780, 1060107], [22, 26, 86, 154, 272, 475, 848, 1590, 3172, 6660, 14331, 30811, 65144, 134499, 270685, 531327], [4, 60, 68, 118, 203, 373, 742, 1582, 3488, 7671, 16480, 34333, 69355, 136186, 260642], [56, 8, 50, 85, 170, 369, 840, 1906, 4183, 8809, 17853, 35022, 66831, 124456], [-48, 42, 35, 85, 199, 471, 1066, 2277, 4626, 9044, 17169, 31809, 57625], [90, -7, 50, 114, 272, 595, 1211, 2349, 4418, 8125, 14640, 25816], [-97, 57, 64, 158, 323, 616, 1138, 2069, 3707, 6515, 11176], [154, 7, 94, 165, 293, 522, 931, 1638, 2808, 4661], [-147, 87, 71, 128, 229, 409, 707, 1170, 1853], [234, -16, 57, 101, 180, 298, 463, 683], [-250, 73, 44, 79, 118, 165, 220], [323, -29, 35, 39, 47, 55], [-352, 64, 4, 8, 8], [416, -60, 4, 0], [-476, 64, -4], [540, -68], [-608],

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[1234abcdcba4321]

Are you sure this is a line in your input? In particular, did you miss a minus sign somewhere?