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diff --git a/src/2017/day22/README.md b/src/2017/day22/README.md index 56b870e..ae4f649 100644 --- a/src/2017/day22/README.md +++ b/src/2017/day22/README.md @@ -84,4 +84,88 @@ By this time, 41 bursts of activity caused an infection (though most of those no After a total of 10000 bursts of activity, 5587 bursts will have caused an infection. Given your actual map, after 10000 bursts of activity, how many bursts cause a node to become infected? (Do not count nodes that begin infected.) +--- Part Two --- +As you go to remove the virus from the infected nodes, it evolves to resist your attempt. +Now, before it infects a clean node, it will weaken it to disable your defenses. If it encounters an infected node, it will instead flag the node to be cleaned in the future. So: + +Clean nodes become weakened. +Weakened nodes become infected. +Infected nodes become flagged. +Flagged nodes become clean. +Every node is always in exactly one of the above states. + +The virus carrier still functions in a similar way, but now uses the following logic during its bursts of action: + +Decide which way to turn based on the current node: +If it is clean, it turns left. +If it is weakened, it does not turn, and will continue moving in the same direction. +If it is infected, it turns right. +If it is flagged, it reverses direction, and will go back the way it came. +Modify the state of the current node, as described above. +The virus carrier moves forward one node in the direction it is facing. +Start with the same map (still using . for clean and # for infected) and still with the virus carrier starting in the middle and facing up. + +Using the same initial state as the previous example, and drawing weakened as W and flagged as F, the middle of the infinite grid looks like this, with the virus carrier's position again marked with [ ]: + +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +. . . . . # . . . +. . . #[.]. . . . +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +This is the same as before, since no initial nodes are weakened or flagged. The virus carrier is on a clean node, so it still turns left, instead weakens the node, and moves left: + +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +. . . . . # . . . +. . .[#]W . . . . +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +The virus carrier is on an infected node, so it still turns right, instead flags the node, and moves up: + +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +. . .[.]. # . . . +. . . F W . . . . +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +This process repeats three more times, ending on the previously-flagged node and facing right: + +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +. . W W . # . . . +. . W[F]W . . . . +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +Finding a flagged node, it reverses direction and cleans the node: + +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +. . W W . # . . . +. .[W]. W . . . . +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +The weakened node becomes infected, and it continues in the same direction: + +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +. . W W . # . . . +.[.]# . W . . . . +. . . . . . . . . +. . . . . . . . . +. . . . . . . . . +Of the first 100 bursts, 26 will result in infection. Unfortunately, another feature of this evolved virus is speed; of the first 10000000 bursts, 2511944 will result in infection. + +Given your actual map, after 10000000 bursts of activity, how many bursts cause a node to become infected? (Do not count nodes that begin infected.) |