--- /dev/null
+# Laser display boards
+
+You're off on your first sightseening trip of your holiday and you need to catch the right llama-rickshaw to get there. You arrive all keen at the llama-rickshaw station, only to find a scene of chaos. The bad news is that there are lots of llama-rickshaws heading to different places. The good news is that above each bay is a display board that shows where that llama-rickshaw is heading. The bad news is that all the display boards have gone down. The good news is that the station staff are handing out the machine-code instructions to generate the messages on the board.
+
+Given your l33t haxor skilz, it will be no problem to recreate the messages on the display boards.
+
+The board is grid, 80 pixels wide and 8 pixels tall, with row 1 being the top row and column 1 being the left column. The pixels are changed with these commands:
+
+* `top A B` switches the state of the pixels in the topmost row from columns A to B inclusive. If a pixel was lit, it becomes dark; if it was dark, it becomes lit.
+* `left A B` is similar, but works on the left edge, toggling the state of pixels in the leftmost column in rows A to B inclusive.
+* `rotate column A B` rotates column A by B spaces down. Pixels that are moved beyond the bottom edge "wrap around" to the top edge.
+* `rotate row A B` rotates row A by B spaces to the right. Pixels that are moved beyond the right edge "wrap around" to the left edge.
+
+You can assume all numbers are integers, the row and column values are always valid, and `A` $\le$ `B` in the `left` and `top` commands.
+
+For instance, with a smaller grid that is 10 pixels wide and 4 tall, this is what a sample sequence of instructions would do.
+
+* `top 1 6` turns on the first six pixels on the top row.
+```
+******....
+..........
+..........
+..........
+```
+
+* `rotate column 2 3` moves the lit pixel on the second column to the bottom row.
+```
+*.****....
+..........
+..........
+.*........
+```
+
+* `top 3 10` turns off the pixels in columns 4, 5, and 6, and turns on the pixels in columns 7 to 10.
+
+```
+*.....****
+..........
+..........
+.*........
+```
+
+* `rotate column 8 5` moves the one lit pixel in column 8 down five rows, wrapping it all the way around the display and leaving the board with one lit pixel in that column one row lower.
+```
+*.....*.**
+.......*..
+..........
+.*........
+```
+
+* `rotate row 2 6` moves that pixel off the right edge of the display, to it wraps around to appear in column 4.
+```
+*.....*.**
+...*......
+..........
+.*........
+```
+
+* `left 1 3` toggles the pixels in rows 1, 2, and 3 of the first column. The top left pixel (previously on) turns off, while the pixels in rows 2 and 3 come on.
+```
+......*.**
+*..*......
+*.........
+.*........
+```
+
projects / ou-summer-of-code-2017.git / blobdiff