## \-\-- Day 22: Sporifica Virus \-\-- Diagnostics indicate that the local *grid computing cluster* has been contaminated with the *Sporifica Virus*. The grid computing cluster is a seemingly-infinite two-dimensional grid of compute nodes. Each node is either *clean* or *infected* by the virus. To [prevent overloading](https://en.wikipedia.org/wiki/Morris_worm#The_mistake) the nodes (which would render them useless to the virus) or detection by system administrators, exactly one *virus carrier* moves through the network, infecting or cleaning nodes as it moves. The virus carrier is always located on a single node in the network (the *current node*) and keeps track of the *direction* it is facing. To avoid detection, the virus carrier works in bursts; in each burst, it *wakes up*, does some *work*, and goes back to *sleep*. The following steps are all executed *in order* one time each burst: - If the *current node* is *infected*, it turns to its *right*. Otherwise, it turns to its *left*. (Turning is done in-place; the *current node* does not change.) - If the *current node* is *clean*, it becomes *infected*. Otherwise, it becomes *cleaned*. (This is done *after* the node is considered for the purposes of changing direction.) - The virus carrier [moves](https://www.youtube.com/watch?v=2vj37yeQQHg) *forward* one node in the direction it is facing. Diagnostics have also provided a *map of the node infection status* (your puzzle input). *Clean* nodes are shown as `.`; *infected* nodes are shown as `#`. This map only shows the center of the grid; there are many more nodes beyond those shown, but none of them are currently infected. The virus carrier begins in the middle of the map facing *up*. For example, suppose you are given a map like this: ..# #.. ... Then, the middle of the infinite grid looks like this, with the virus carrier\'s position marked with `[ ]`: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . # . . . . . . #[.]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The virus carrier is on a *clean* node, so it turns *left*, *infects* the node, and moves left: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . # . . . . . .[#]# . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The virus carrier is on an *infected* node, so it turns *right*, *cleans* the node, and moves up: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .[.]. # . . . . . . . # . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Four times in a row, the virus carrier finds a *clean*, *infects* it, turns *left*, and moves forward, ending in the same place and still facing up: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . #[#]. # . . . . . # # # . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Now on the same node as before, it sees an infection, which causes it to turn *right*, *clean* the node, and move forward: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . # .[.]# . . . . . # # # . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . After the above actions, a total of `7` bursts of activity had taken place. Of them, `5` bursts of activity caused an infection. After a total of `70`, the grid looks like this, with the virus carrier facing up: . . . . . # # . . . . . . # . . # . . . . # . . . . # . . # . #[.]. . # . . # . # . . # . . . . . . # # . . . . . . . . . . . . . . . . . . . . By this time, `41` bursts of activity caused an infection (though most of those nodes have since been cleaned). 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.) Your puzzle answer was `5266`. ## \-\-- Part Two \-\-- {#part2} 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.) Your puzzle answer was `2511895`. Both parts of this puzzle are complete! They provide two gold stars: \*\* At this point, you should [return to your Advent calendar](/2017) and try another puzzle. If you still want to see it, you can [get your puzzle input](22/input).