<filename>day2.py<gh_stars>0
"""
--- Day 2: 1202 Program Alarm ---
On the way to your gravity assist around the Moon,
your ship computer beeps angrily about a "1202 program alarm".
On the radio, an Elf is already explaining how to
handle the situation: "Don't worry, that's perfectly norma--"
The ship computer bursts into flames.

You notify the Elves that the computer's magic smoke seems
to have escaped. "That computer ran Intcode programs like
the gravity assist program it was working on; surely there
are enough spare parts up there to build a new Intcode computer!"

An Intcode program is a list of integers separated by commas (like 1,0,0,3,99).
To run one, start by looking at the first integer (called position 0).
Here, you will find an opcode - either 1, 2, or 99.
The opcode indicates what to do; for example, 99 means that the program
is finished and should immediately halt.
Encountering an unknown opcode means something went wrong.

Opcode 1 adds together numbers read from two positions and
stores the result in a third position.
The three integers immediately after the opcode tell you these three positions -
the first two indicate the positions from which you should read the input values, and
the third indicates the position at which the output should be stored.

For example, if your Intcode computer encounters 1,10,20,30, it should read the values
at positions 10 and 20, add those values, and then overwrite the value at position 30 with their sum.

Opcode 2 works exactly like opcode 1, except it multiplies the two
inputs instead of adding them. Again, the three integers after the
opcode indicate where the inputs and outputs are, not their values.

Once you're done processing an opcode, move to the next one by stepping forward 4 positions.

For example, suppose you have the following program:

1,9,10,3,2,3,11,0,99,30,40,50
For the purposes of illustration, here is the same program split into multiple lines:

1,9,10,3,
2,3,11,0,
99,
30,40,50
The first four integers, 1,9,10,3, are at positions 0, 1, 2, and 3.
Together, they represent the first opcode (1, addition), the positions
of the two inputs (9 and 10), and the position of the output (3).
To handle this opcode, you first need to get the values at the input
positions: position 9 contains 30, and position 10 contains 40.
Add these numbers together to get 70. Then, store this value at
the output position; here, the output position (3) is at position 3,
so it overwrites itself. Afterward, the program looks like this:

1,9,10,70,
2,3,11,0,
99,
30,40,50
Step forward 4 positions to reach the next opcode, 2. This opcode works
just like the previous, but it multiplies instead of adding. The inputs
are at positions 3 and 11; these positions contain 70 and 50 respectively.
Multiplying these produces 3500; this is stored at position 0:

3500,9,10,70,
2,3,11,0,
99,
30,40,50
Stepping forward 4 more positions arrives at opcode 99, halting the program.

Here are the initial and final states of a few more small programs:

1,0,0,0,99 becomes 2,0,0,0,99 (1 + 1 = 2).
2,3,0,3,99 becomes 2,3,0,6,99 (3 * 2 = 6).
2,4,4,5,99,0 becomes 2,4,4,5,99,9801 (99 * 99 = 9801).
1,1,1,4,99,5,6,0,99 becomes 30,1,1,4,2,5,6,0,99.
Once you have a working computer, the first step is to restore the
gravity assist program (your puzzle input) to the "1202 program alarm"
state it had just before the last computer caught fire. To do this,
before running the program, replace position 1 with the value 12 and
replace position 2 with the value 2. What value is left at position 0 after the program halts?

--- Part Two ---
"Good, the new computer seems to be working correctly!
Keep it nearby during this mission - you'll probably
use it again. Real Intcode computers support many
more features than your new one, but we'll let you
know what they are as you need them."

"However, your current priority should be to complete
your gravity assist around the Moon. For this mission
to succeed, we should settle on some terminology for
the parts you've already built."

Intcode programs are given as a list of integers;
these values are used as the initial state for the
computer's memory. When you run an Intcode program,
make sure to start by initializing memory to the
program's values. A position in memory is called an
address (for example, the first value in memory
is at "address 0").

Opcodes (like 1, 2, or 99) mark the beginning of an
instruction. The values used immediately after an
opcode, if any, are called the instruction's parameters.
For example, in the instruction 1,2,3,4, 1 is the
opcode; 2, 3, and 4 are the parameters.
The instruction 99 contains only an
opcode and has no parameters.

The address of the current instruction is called
the instruction pointer; it starts at 0. After an
instruction finishes, the instruction pointer
increases by the number of values in the instruction;
until you add more instructions to the computer, this
is always 4 (1 opcode + 3 parameters) for the add and
multiply instructions. (The halt instruction would
increase the instruction pointer by 1, but it halts
the program instead.)

"With terminology out of the way, we're ready to proceed.
To complete the gravity assist, you need to determine
what pair of inputs produces the output 19690720."

The inputs should still be provided to the program by
replacing the values at addresses 1 and 2, just like
before. In this program, the value placed in address
1 is called the noun, and the value placed in
address 2 is called the verb. Each of the two input
values will be between 0 and 99, inclusive.

Once the program has halted, its output is available
at address 0, also just like before. Each time you
try a pair of inputs, make sure you first reset the
computer's memory to the values in the program (your
puzzle input) - in other words, don't reuse memory
from a previous attempt.

Find the input noun and verb that cause the program
to produce the output 19690720. What is 100 * noun + verb?
(For example, if noun=12 and verb=2, the answer would be 1202.)
"""

from typing import List

ADD, MUL, STOP = 1, 2, 99


def part1(arr, noun=12, verb=2):
    return run_opcodes(arr, noun, verb)


def run_opcodes(arr, noun, verb):
    arr[1] = noun
    arr[2] = verb
    i = 0
    while i < len(arr) and arr[i] != 99:
        if arr[i] >= len(arr) or arr[i+1] >= len(arr) or arr[i+2] >= len(arr) or arr[i+3] >= len(arr):
            return -1
        if arr[i] == ADD:
            arr[arr[i + 3]] = arr[arr[i + 1]] + arr[arr[i + 2]]
        elif arr[i] == MUL:
            arr[arr[i + 3]] = arr[arr[i + 1]] * arr[arr[i + 2]]
        elif arr[i] == STOP:
            return arr[0]
        i += 4
    return arr[0]


def part2(arr, val):
    for n in range(99):
        for v in range(99):
            a = list(arr)
            res = run_opcodes(a, n, v)
            if res == val:
                return n, v
    return -1, -1


def day2():
    arr = [
        1, 0, 0, 3, 1, 1, 2, 3, 1, 3, 4, 3, 1, 5, 0, 3, 2, 10, 1, 19, 1, 19, 5, 23, 1, 23, 9, 27, 2, 27, 6, 31, 1, 31,
        6, 35, 2, 35, 9, 39, 1, 6, 39, 43, 2, 10, 43, 47, 1, 47, 9, 51, 1, 51, 6, 55, 1, 55, 6, 59, 2, 59, 10, 63, 1, 6,
        63, 67, 2, 6, 67, 71, 1, 71, 5, 75, 2, 13, 75, 79, 1, 10, 79, 83, 1, 5, 83, 87, 2, 87, 10, 91, 1, 5, 91, 95, 2,
        95, 6, 99, 1, 99, 6, 103, 2, 103, 6, 107, 2, 107, 9, 111, 1, 111, 5, 115, 1, 115, 6, 119, 2, 6, 119, 123, 1, 5,
        123, 127, 1, 127, 13, 131, 1, 2, 131, 135, 1, 135, 10, 0, 99, 2, 14, 0, 0
    ]

    print(part1(list(arr)))

    noun, verb = part2(list(arr), 19690720)
    print(100 * noun + verb)


if __name__ == '__main__':
    day2()
