part1 (4931B)
1--- Day 10: The Stars Align --- 2 3It's no use; your navigation system simply isn't capable of providing walking directions in the 4arctic circle, and certainly not in 1018. 5 6The Elves suggest an alternative. In times like these, North Pole rescue operations will arrange 7points of light in the sky to guide missing Elves back to base. Unfortunately, the message is easy 8to miss: the points move slowly enough that it takes hours to align them, but have so much momentum 9that they only stay aligned for a second. If you blink at the wrong time, it might be hours before 10another message appears. 11 12You can see these points of light floating in the distance, and record their position in the sky and 13their velocity, the relative change in position per second (your puzzle input). The coordinates are 14all given from your perspective; given enough time, those positions and velocities will move the 15points into a cohesive message! 16 17Rather than wait, you decide to fast-forward the process and calculate what the points will 18eventually spell. 19 20For example, suppose you note the following points: 21 22position=< 9, 1> velocity=< 0, 2> 23position=< 7, 0> velocity=<-1, 0> 24position=< 3, -2> velocity=<-1, 1> 25position=< 6, 10> velocity=<-2, -1> 26position=< 2, -4> velocity=< 2, 2> 27position=<-6, 10> velocity=< 2, -2> 28position=< 1, 8> velocity=< 1, -1> 29position=< 1, 7> velocity=< 1, 0> 30position=<-3, 11> velocity=< 1, -2> 31position=< 7, 6> velocity=<-1, -1> 32position=<-2, 3> velocity=< 1, 0> 33position=<-4, 3> velocity=< 2, 0> 34position=<10, -3> velocity=<-1, 1> 35position=< 5, 11> velocity=< 1, -2> 36position=< 4, 7> velocity=< 0, -1> 37position=< 8, -2> velocity=< 0, 1> 38position=<15, 0> velocity=<-2, 0> 39position=< 1, 6> velocity=< 1, 0> 40position=< 8, 9> velocity=< 0, -1> 41position=< 3, 3> velocity=<-1, 1> 42position=< 0, 5> velocity=< 0, -1> 43position=<-2, 2> velocity=< 2, 0> 44position=< 5, -2> velocity=< 1, 2> 45position=< 1, 4> velocity=< 2, 1> 46position=<-2, 7> velocity=< 2, -2> 47position=< 3, 6> velocity=<-1, -1> 48position=< 5, 0> velocity=< 1, 0> 49position=<-6, 0> velocity=< 2, 0> 50position=< 5, 9> velocity=< 1, -2> 51position=<14, 7> velocity=<-2, 0> 52position=<-3, 6> velocity=< 2, -1> 53 54Each line represents one point. Positions are given as <X, Y> pairs: X represents how far left 55(negative) or right (positive) the point appears, while Y represents how far up (negative) or down 56(positive) the point appears. 57 58At 0 seconds, each point has the position given. Each second, each point's velocity is added to its 59position. So, a point with velocity <1, -2> is moving to the right, but is moving upward twice as 60quickly. If this point's initial position were <3, 9>, after 3 seconds, its position would become 61<6, 3>. 62 63Over time, the points listed above would move like this: 64 65Initially: 66........#............. 67................#..... 68.........#.#..#....... 69...................... 70#..........#.#.......# 71...............#...... 72....#................. 73..#.#....#............ 74.......#.............. 75......#............... 76...#...#.#...#........ 77....#..#..#.........#. 78.......#.............. 79...........#..#....... 80#...........#......... 81...#.......#.......... 82 83After 1 second: 84...................... 85...................... 86..........#....#...... 87........#.....#....... 88..#.........#......#.. 89...................... 90......#............... 91....##.........#...... 92......#.#............. 93.....##.##..#......... 94........#.#........... 95........#...#.....#... 96..#...........#....... 97....#.....#.#......... 98...................... 99...................... 100 101After 2 seconds: 102...................... 103...................... 104...................... 105..............#....... 106....#..#...####..#.... 107...................... 108........#....#........ 109......#.#............. 110.......#...#.......... 111.......#..#..#.#...... 112....#....#.#.......... 113.....#...#...##.#..... 114........#............. 115...................... 116...................... 117...................... 118 119After 3 seconds: 120...................... 121...................... 122...................... 123...................... 124......#...#..###...... 125......#...#...#....... 126......#...#...#....... 127......#####...#....... 128......#...#...#....... 129......#...#...#....... 130......#...#...#....... 131......#...#..###...... 132...................... 133...................... 134...................... 135...................... 136 137After 4 seconds: 138...................... 139...................... 140...................... 141............#......... 142........##...#.#...... 143......#.....#..#...... 144.....#..##.##.#....... 145.......##.#....#...... 146...........#....#..... 147..............#....... 148....#......#...#...... 149.....#.....##......... 150...............#...... 151...............#...... 152...................... 153...................... 154 155After 3 seconds, the message appeared briefly: [1m[97mHI[0m. Of course, your message will be much longer and 156will take many more seconds to appear. 157 158[1m[97mWhat message will eventually appear in the sky?[0m 159 160