2021 Day 07

2021/07/README.md

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+# 2021 Day 07: The Treachery of Whales
+Copyright (c) Eric Wastl
+#### [Direct Link](https://adventofcode.com/2021/day/07)
+
+## Part 1
+
+A giant [whale](https://en.wikipedia.org/wiki/Sperm_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?**
+
+## Part 2
+
+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?**

2021/07/code.py

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+# SPDX-License-Identifier: MIT
+# Copyright (c) 2021 Akumatic
+#
+# https://adventofcode.com/2021/day/06
+
+def read_file(filename: str = "input.txt") -> list:
+    with open(f"{__file__.rstrip('code.py')}{filename}", "r") as f:
+        return [int(x) for x in f.read().strip().split(",")]
+
+def calculate_distances(positions):
+    return [[abs(p-r) for p in positions] for r in range(min(positions), max(positions)+1)]
+
+def part1(vals: list) -> int:
+    return min(sum(dists) for dists in calculate_distances(vals))
+
+def part2(vals: list) -> int:
+    return min(sum((d*d+d)//2 for d in dists) for dists in calculate_distances(vals))
+                
+if __name__ == "__main__":
+    vals = read_file()
+    print(f"Part 1: {part1(vals)}")
+    print(f"Part 2: {part2(vals)}")

2021/07/input.txt

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+1101,1,29,67,1102,0,1,65,1008,65,35,66,1005,66,28,1,67,65,20,4,0,1001,65,1,65,1106,0,8,99,35,67,101,99,105,32,110,39,101,115,116,32,112,97,115,32,117,110,101,32,105,110,116,99,111,100,101,32,112,114,111,103,114,97,109,10,27,591,29,1713,943,341,593,941,152,142,746,674,269,241,20,8,991,662,34,24,669,34,233,137,576,215,957,570,553,111,205,210,27,1397,941,31,246,1064,83,53,285,517,972,29,742,34,260,185,1582,1273,248,1132,346,1208,146,171,220,1769,47,735,719,12,39,517,694,253,293,244,31,133,163,22,47,20,166,190,1072,24,17,445,250,6,139,134,361,304,812,201,825,87,118,1213,710,132,261,184,37,512,90,1276,1007,83,132,874,0,109,1005,513,1544,1759,1447,351,1172,1087,1392,643,872,3,882,805,547,1360,20,33,5,844,411,121,167,586,5,39,230,1321,1058,197,244,178,12,900,257,21,346,280,225,571,717,62,55,368,120,254,695,766,55,534,266,9,273,1,466,203,870,1188,623,15,135,538,779,698,83,850,1244,63,562,19,1050,6,495,243,1388,293,38,80,265,261,1392,351,505,922,434,644,721,97,227,635,753,467,6,1649,945,1405,492,332,789,414,440,791,105,778,1851,959,80,291,1077,434,928,272,156,72,321,180,1281,78,15,603,1243,306,533,1024,637,719,62,378,3,339,1805,1236,647,92,574,63,418,1342,226,85,532,9,19,893,155,1686,350,54,161,51,437,1096,508,137,920,20,146,824,142,233,328,286,289,229,90,89,760,1005,557,7,510,1572,64,1378,0,624,15,476,368,885,1264,260,312,141,799,1303,1136,706,54,1612,395,84,508,201,213,241,293,74,132,350,652,291,239,119,184,840,594,310,588,129,330,311,8,177,366,379,522,527,1332,857,853,621,560,464,339,2,839,582,23,466,1415,325,971,582,118,391,1098,640,1351,201,800,1579,332,100,196,1,238,1078,157,599,378,392,1433,34,366,473,193,90,106,245,393,164,1751,1054,697,749,389,1060,66,604,190,444,54,1273,175,65,1188,1977,829,744,918,66,1023,404,1436,1392,26,366,98,1038,254,304,723,21,606,349,5,645,610,1626,287,523,411,826,155,457,230,1124,648,271,567,671,71,918,20,16,787,975,785,133,132,330,278,2,1460,493,696,1264,40,319,691,332,1258,26,213,1024,389,688,183,162,604,993,539,75,998,362,466,1033,647,78,103,666,1338,1158,1397,319,1073,416,1274,9,52,302,83,427,546,132,228,499,7,829,77,76,271,68,1,1388,874,521,530,594,531,710,7,1104,85,832,30,7,285,40,1414,140,243,141,1613,575,805,709,627,310,97,1093,377,364,876,283,176,545,57,300,3,1255,360,1100,90,87,1017,28,9,1094,112,1339,20,713,134,345,559,138,1078,116,874,334,485,756,585,872,846,1072,262,11,1285,95,1658,36,79,308,13,221,364,264,571,110,605,102,465,3,194,619,310,890,880,724,26,330,378,44,1430,642,328,89,527,111,420,1239,93,46,267,379,18,238,1373,303,833,521,761,30,748,343,630,289,84,1160,789,45,100,734,204,275,1543,1072,1787,105,87,0,164,719,354,284,309,1743,1608,41,259,343,76,515,310,661,986,114,203,711,73,297,98,1346,372,166,1073,111,910,679,289,56,46,114,430,411,326,48,1117,10,330,666,107,389,68,995,171,1690,161,1051,1362,741,361,418,702,956,1311,621,277,816,604,160,19,1298,25,585,189,1259,697,89,128,543,1148,27,270,165,1005,1022,400,38,423,467,43,967,1242,133,719,7,1,348,597,79,122,126,168,312,898,158,1,162,133,455,366,62,6,1159,346,529,505,29,503,177,749,190,910,386,274,1284,525,520,981,743,603,17,597,330,183,276,445,380,360,936,1562,1007,35,492,129,716,374,412,518,117,4,1469,713,356,92,7,372,113,128,164,359,1409,1147,543,8,179,232,1356,1131,168,579,133,174,1357,1601,21,104,365,7,32,1052,1656,1313,396,171,688,840,115,370,766,309,1477,38,556,5,1696,284,310,217,158,127,208,75,443,241,120,76,13,948,227,855,29,362,362,535,313,882,233,514,152,380,630,63,29,233,1623,862,139,21,828,119,154,130,1057,542,226,868,89,160,1267,346,209,1067,1001,92,170,104,557,634,161,1825,717,622,51,190,600,22,114,902,11,3,388,1773,523,224,1455,773,283,56,102,207,23,840,67,743,407,1017,957,94,33,38,710,176,115,926,537,338,606,257,957,1573,1270,222,591,714,1430,209,250,17,69,917,1270,81,648,96,74,232,426,299,598,41,1125,1108,50,521,209,327,452,281,609,124,1124,606,1395,554,754,15,559,174,786,1325,634,133,93,398

2021/07/solution.txt

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+Part 1: 347509
+Part 2: 98257206

2021/07/test_code.py

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+# SPDX-License-Identifier: MIT
+# Copyright (c) 2021 Akumatic
+
+from code import part1, part2, read_file
+
+def test():
+    vals = read_file("test_input.txt")
+    assert part1(vals) == 37
+    print("Passed Part 1")
+    assert part2(vals) == 168
+    print("Passed Part 2")
+
+if __name__ == "__main__":
+    test()

2021/07/test_input.txt

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

2021/README.md

@@ -21,7 +21,7 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 | 04 | :white_check_mark: | :white_check_mark: | [Solution](04/code.py) | [Day 04](https://adventofcode.com/2021/day/4) |
 | 05 | :white_check_mark: | :white_check_mark: | [Solution](05/code.py) | [Day 05](https://adventofcode.com/2021/day/5) |
 | 06 | :white_check_mark: | :white_check_mark: | [Solution](06/code.py) | [Day 06](https://adventofcode.com/2021/day/6) |
-| 07 |  |  |  |  |
+| 07 | :white_check_mark: | :white_check_mark: | [Solution](07/code.py) | [Day 07](https://adventofcode.com/2021/day/7) |
 | 08 |  |  |  |  |
 | 09 |  |  |  |  |
 | 10 |  |  |  |  |