From: Neil Smith Date: Tue, 7 Dec 2021 10:35:25 +0000 (+0000) Subject: Done day 7 X-Git-Url: https://git.njae.me.uk/?a=commitdiff_plain;h=ff87f3bf728b1af9044520f39e34e0548438b8ca;p=advent-of-code-21.git Done day 7 --- diff --git a/advent-of-code21.cabal b/advent-of-code21.cabal index c19d0d4..11a6fbd 100644 --- a/advent-of-code21.cabal +++ b/advent-of-code21.cabal @@ -109,3 +109,8 @@ executable advent06 import: common-extensions, build-directives main-is: advent06/Main.hs build-depends: split, containers + +executable advent07 + import: common-extensions, build-directives + main-is: advent07/Main.hs + build-depends: split diff --git a/advent07/Main.hs b/advent07/Main.hs new file mode 100644 index 0000000..50cd076 --- /dev/null +++ b/advent07/Main.hs @@ -0,0 +1,36 @@ +-- Writeup at https://work.njae.me.uk/2021/12/07/advent-of-code-2021-day-7/ + +import Data.List.Split + +main :: IO () +main = + do text <- readFile "data/advent07.txt" + let subs = map (read @Int) $ splitOn "," text + print $ part1 subs + print $ part2 subs + +part1 = bestFuel loss1 +part2 = bestFuel loss2 + +bestFuel :: ([Int] -> Int -> Int) -> [Int] -> Int +bestFuel loss subs = loss subs best + where meanSub = (sum subs) `div` (length subs) + best = gradientDescend loss subs meanSub + +loss1 :: [Int] -> Int -> Int +loss1 subs target = sum $ map diff subs + where diff s = abs (target - s) + +loss2 :: [Int] -> Int -> Int +loss2 subs target = sum $ map triangleDiff subs + where diff s = abs (target - s) + triangleDiff s = ((diff s) * ((diff s) + 1)) `div` 2 + +gradientDescend :: ([Int] -> Int -> Int) -> [Int] -> Int -> Int +gradientDescend loss subs guess = + if | lossLower < lossHere -> gradientDescend loss subs (guess - 1) + | lossHigher < lossHere -> gradientDescend loss subs (guess + 1) + | otherwise -> guess + where lossHere = loss subs guess + lossLower = loss subs (guess - 1) + lossHigher = loss subs (guess + 1) diff --git a/data/advent07.txt b/data/advent07.txt new file mode 100644 index 0000000..58b0702 --- /dev/null +++ b/data/advent07.txt @@ -0,0 +1 @@ +1101,1,29,67,1102,0,1,65,1008,65,35,66,1005,66,28,1,67,65,20,4,0,1001,65,1,65,1106,0,8,99,35,67,101,99,105,32,110,39,101,115,116,32,112,97,115,32,117,110,101,32,105,110,116,99,111,100,101,32,112,114,111,103,114,97,109,10,616,0,1633,1048,833,967,161,22,823,601,603,538,340,798,1053,400,54,41,54,296,1336,1013,9,763,650,313,15,177,1289,307,741,314,289,63,183,503,764,187,225,596,273,387,1,1165,61,19,78,514,355,605,103,483,291,1781,1137,398,593,38,444,204,274,528,147,131,1021,812,430,710,257,1408,1587,517,773,218,99,357,301,543,1668,11,311,350,373,145,507,325,1006,696,607,281,433,302,148,519,846,1528,766,158,51,850,216,1320,690,338,298,631,560,306,5,888,242,1230,1694,1330,570,184,946,97,96,272,537,312,1246,847,138,325,28,253,785,483,906,412,28,178,485,828,823,1035,1001,108,1068,90,308,223,18,191,1269,39,238,307,7,643,1546,203,254,371,402,207,666,786,793,361,441,105,15,421,1748,255,152,1376,626,296,707,4,627,885,49,316,34,379,1591,39,1087,135,1515,69,725,419,924,414,78,1169,8,1331,2,771,1295,570,323,9,406,75,42,1003,180,188,174,145,128,625,1312,85,427,56,15,87,449,831,906,34,186,609,1597,531,104,1034,615,608,1338,192,280,982,334,853,1155,194,124,205,1384,135,906,239,761,1357,16,328,623,3,1432,634,1698,31,981,347,75,222,896,77,1204,1272,711,106,772,1366,279,162,98,487,1281,188,71,307,398,470,40,12,459,449,984,1271,260,1132,493,1117,129,36,1040,947,570,89,853,373,102,771,107,266,106,59,485,61,87,353,164,278,1489,542,442,4,62,788,63,130,723,919,1169,327,459,431,1107,992,1162,1287,901,838,638,261,307,761,533,119,336,4,422,173,172,64,222,531,998,1250,1007,20,1231,69,289,531,757,185,519,184,1139,369,2,1102,857,339,1267,1357,217,774,1352,23,136,2,1389,253,87,883,28,247,292,15,332,69,170,20,544,75,850,310,1137,301,155,265,100,842,189,7,584,40,168,22,548,7,30,1027,744,1294,329,100,1255,424,515,460,163,375,26,618,275,1012,935,160,181,84,186,990,1208,152,753,508,590,578,81,625,600,430,306,311,156,5,56,187,25,249,1090,316,224,173,199,71,221,1219,335,87,260,607,121,25,1326,473,224,92,87,734,179,64,325,320,117,302,1247,879,716,984,284,239,738,30,90,61,844,997,823,387,956,842,580,540,648,1947,32,63,380,873,1086,142,512,206,742,584,157,858,1300,992,311,139,906,693,1,36,1320,236,48,58,32,147,34,229,497,1,657,616,309,494,1419,264,595,729,1374,984,74,446,436,77,1516,156,915,565,159,269,263,442,775,12,6,337,115,971,598,87,1283,533,991,204,1382,1204,277,27,801,260,198,426,89,72,458,1164,571,1329,501,1547,125,376,865,642,268,626,167,429,901,623,103,100,1064,125,450,695,28,1470,469,187,119,1363,44,485,1243,1163,507,139,147,72,100,160,624,506,1360,66,444,581,729,531,701,1091,178,476,22,926,354,88,1076,946,213,38,43,125,291,714,113,54,1214,1067,641,374,411,64,1364,415,133,752,372,212,19,1941,780,902,512,852,157,8,175,90,913,125,771,764,381,947,572,391,313,249,201,106,1500,487,107,868,464,984,1471,550,642,196,571,18,306,293,659,1274,290,352,0,528,754,564,316,685,57,293,75,584,251,1107,217,11,21,329,493,175,600,259,380,30,148,556,136,180,12,26,507,199,3,0,143,87,1452,359,989,170,64,269,17,1018,105,317,289,127,275,269,359,511,690,205,423,356,19,177,260,789,51,119,210,1151,707,869,194,773,159,216,759,16,161,47,1254,293,54,504,432,1230,213,26,253,424,98,1515,162,346,326,12,122,79,210,912,55,705,597,369,1381,284,1163,316,34,384,36,1254,1455,994,60,1395,476,100,38,726,198,605,103,489,361,9,24,158,1056,264,1103,175,1423,266,45,93,271,331,673,788,48,12,580,697,593,480,268,559,302,87,281,6,401,170,90,939,543,223,137,809,139,182,571,68,1112,20,1004,1090,249,1435,267,10,375,504,906,946,1503,1362,184,233,112,1058,16,235,548,563,162,102,746,439,105,259,27,19,817,1444,119,175,341,130,202,31,432,480,710,1127,682,454,134,823,168,276,113,914,1112,118,10,1041,902,141,1428,282,485,353,589,906,987,488,144,154,25,930,368,261,176,168,85,814,1915,248,49,1012,3,143,951,30,411,336,46,1383,26,857,1650,192,1477,194,73,154,91,287,229,144,675,989,135,360,74,60,223,219,625,182,793 \ No newline at end of file diff --git a/problems/day07.html b/problems/day07.html new file mode 100644 index 0000000..77f0664 --- /dev/null +++ b/problems/day07.html @@ -0,0 +1,161 @@ + + + + +Day 7 - Advent of Code 2021 + + + + + + + +

Advent of Code

Neil Smith (AoC++) 14*

      /^2021$/

+ + + +
+ +

--- Day 7: The Treachery of Whales ---

A giant whale has decided your submarine is its next meal, and it's much faster than you are. There's nowhere to run!

+

Suddenly, a swarm of crabs (each in its own tiny submarine - it's too deep for them otherwise) zooms in to rescue you! They seem to be preparing to blast a hole in the ocean floor; sensors indicate a massive underground cave system just beyond where they're aiming!

+

The crab submarines all need to be aligned before they'll have enough power to blast a large enough hole for your submarine to get through. However, it doesn't look like they'll be aligned before the whale catches you! Maybe you can help?

+

There's one major catch - crab submarines can only move horizontally.

+

You quickly make a list of the horizontal position of each crab (your puzzle input). Crab submarines have limited fuel, so you need to find a way to make all of their horizontal positions match while requiring them to spend as little fuel as possible.

+

For example, consider the following horizontal positions:

+
16,1,2,0,4,2,7,1,2,14
+

This means there's a crab with horizontal position 16, a crab with horizontal position 1, and so on.

+

Each change of 1 step in horizontal position of a single crab costs 1 fuel. You could choose any horizontal position to align them all on, but the one that costs the least fuel is horizontal position 2:

+
    +
  • Move from 16 to 2: 14 fuel
    • +
  • Move from 1 to 2: 1 fuel
    • +
  • Move from 2 to 2: 0 fuel
    • +
  • Move from 0 to 2: 2 fuel
    • +
  • Move from 4 to 2: 2 fuel
    • +
  • Move from 2 to 2: 0 fuel
    • +
  • Move from 7 to 2: 5 fuel
    • +
  • Move from 1 to 2: 1 fuel
    • +
  • Move from 2 to 2: 0 fuel
    • +
  • Move from 14 to 2: 12 fuel
    • +
+

This costs a total of 37 fuel. This is the cheapest possible outcome; more expensive outcomes include aligning at position 1 (41 fuel), position 3 (39 fuel), or position 10 (71 fuel).

+

Determine the horizontal position that the crabs can align to using the least fuel possible. How much fuel must they spend to align to that position?

+
+

Your puzzle answer was 336721.

--- Part Two ---

The crabs don't seem interested in your proposed solution. Perhaps you misunderstand crab engineering?

+

As it turns out, crab submarine engines don't burn fuel at a constant rate. Instead, each change of 1 step in horizontal position costs 1 more unit of fuel than the last: the first step costs 1, the second step costs 2, the third step costs 3, and so on.

+

As each crab moves, moving further becomes more expensive. This changes the best horizontal position to align them all on; in the example above, this becomes 5:

+
    +
  • Move from 16 to 5: 66 fuel
    • +
  • Move from 1 to 5: 10 fuel
    • +
  • Move from 2 to 5: 6 fuel
    • +
  • Move from 0 to 5: 15 fuel
    • +
  • Move from 4 to 5: 1 fuel
    • +
  • Move from 2 to 5: 6 fuel
    • +
  • Move from 7 to 5: 3 fuel
    • +
  • Move from 1 to 5: 10 fuel
    • +
  • Move from 2 to 5: 6 fuel
    • +
  • Move from 14 to 5: 45 fuel
    • +
+

This costs a total of 168 fuel. This is the new cheapest possible outcome; the old alignment position (2) now costs 206 fuel instead.

+

Determine the horizontal position that the crabs can align to using the least fuel possible so they can make you an escape route! How much fuel must they spend to align to that position?

+
+

Your puzzle answer was 91638945.

Both parts of this puzzle are complete! They provide two gold stars: **

+

At this point, you should return to your Advent calendar and try another puzzle.

+

If you still want to see it, you can get your puzzle input.

+

You can also this puzzle.

+
+ + + + + + \ No newline at end of file