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Day 8: I Heard You Like Registers
You receive a signal directly from the CPU. Because of your recent assistance with jump instructions, it would like you to compute the result of a series of unusual register instructions.
Each instruction consists of several parts: the register to modify, whether to increase or
decrease that register’s value, the amount by which to increase or decrease it, and a condition.
If the condition fails, skip the instruction without modifying the register. The registers all
start at 0
. The instructions look like this:
b inc 5 if a > 1
a inc 1 if b < 5
c dec -10 if a >= 1
c inc -20 if c == 10
These instructions would be processed as follows:
- Because
a
starts at0
, it is not greater than1
, and sob
is not modified. a
is increased by1
(to1
) becauseb
is less than5
(it is0
).c
is decreased by-10
(to10
) becausea
is now greater than or equal to1
(it is1
).c
is increased by-20
(to-10
) becausec
is equal to10
.
After this process, the largest value in any register is 1
.
You might also encounter <=
(less than or equal to) or !=
(not equal to). However, the CPU
doesn’t have the bandwidth to tell you what all the registers are named, and leaves that to you
to determine.
What is the largest value in any register after completing the instructions in your puzzle input?
Part Two
To be safe, the CPU also needs to know the highest value held in any register during this
process so that it can decide how much memory to allocate to these operations. For example, in
the above instructions, the highest value ever held was 10
(in register c
after the third
instruction was evaluated).