159 lines
7.4 KiB
Plaintext
159 lines
7.4 KiB
Plaintext
Advent of Code
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--- Day 2: 1202 Program Alarm ---
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On the way to your gravity assist around the Moon, your ship computer beeps
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angrily about a "1202 program alarm". On the radio, an Elf is already
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explaining how to handle the situation: "Don't worry, that's perfectly
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norma--" The ship computer bursts into flames.
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You notify the Elves that the computer's magic smoke seems to have escaped.
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"That computer ran Intcode programs like the gravity assist program it was
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working on; surely there are enough spare parts up there to build a new
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Intcode computer!"
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An Intcode program is a list of integers separated by commas (like
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1,0,0,3,99). To run one, start by looking at the first integer (called
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position 0). Here, you will find an opcode - either 1, 2, or 99. The opcode
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indicates what to do; for example, 99 means that the program is finished and
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should immediately halt. Encountering an unknown opcode means something went
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wrong.
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Opcode 1 adds together numbers read from two positions and stores the result
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in a third position. The three integers immediately after the opcode tell
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you these three positions - the first two indicate the positions from which
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you should read the input values, and the third indicates the position at
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which the output should be stored.
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For example, if your Intcode computer encounters 1,10,20,30, it should read
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the values at positions 10 and 20, add those values, and then overwrite the
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value at position 30 with their sum.
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Opcode 2 works exactly like opcode 1, except it multiplies the two inputs
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instead of adding them. Again, the three integers after the opcode indicate
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where the inputs and outputs are, not their values.
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Once you're done processing an opcode, move to the next one by stepping
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forward 4 positions.
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For example, suppose you have the following program:
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1,9,10,3,2,3,11,0,99,30,40,50
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For the purposes of illustration, here is the same program split into
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multiple lines:
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1,9,10,3, 2,3,11,0, 99, 30,40,50
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The first four integers, 1,9,10,3, are at positions 0, 1, 2, and 3.
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Together, they represent the first opcode (1, addition), the positions of
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the two inputs (9 and 10), and the position of the output (3). To handle
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this opcode, you first need to get the values at the input positions:
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position 9 contains 30, and position 10 contains 40. Add these numbers
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together to get 70. Then, store this value at the output position; here, the
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output position (3) is at position 3, so it overwrites itself. Afterward,
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the program looks like this:
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1,9,10,70, 2,3,11,0, 99, 30,40,50
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Step forward 4 positions to reach the next opcode, 2. This opcode works just
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like the previous, but it multiplies instead of adding. The inputs are at
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positions 3 and 11; these positions contain 70 and 50 respectively.
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Multiplying these produces 3500; this is stored at position 0:
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3500,9,10,70, 2,3,11,0, 99, 30,40,50
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Stepping forward 4 more positions arrives at opcode 99, halting the program.
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Here are the initial and final states of a few more small programs:
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• 1,0,0,0,99 becomes 2,0,0,0,99 (1 + 1 = 2).
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• 2,3,0,3,99 becomes 2,3,0,6,99 (3 * 2 = 6).
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• 2,4,4,5,99,0 becomes 2,4,4,5,99,9801 (99 * 99 = 9801).
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• 1,1,1,4,99,5,6,0,99 becomes 30,1,1,4,2,5,6,0,99.
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Once you have a working computer, the first step is to restore the gravity
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assist program (your puzzle input) to the "1202 program alarm" state it had
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just before the last computer caught fire. To do this, before running the
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program, replace position 1 with the value 12 and replace position 2 with
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the value 2. What value is left at position 0 after the program halts?
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Your puzzle answer was 4930687.
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--- Part Two ---
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"Good, the new computer seems to be working correctly! Keep it nearby during
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this mission - you'll probably use it again. Real Intcode computers support
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many more features than your new one, but we'll let you know what they are
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as you need them."
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"However, your current priority should be to complete your gravity assist
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around the Moon. For this mission to succeed, we should settle on some
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terminology for the parts you've already built."
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Intcode programs are given as a list of integers; these values are used as
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the initial state for the computer's memory. When you run an Intcode
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program, make sure to start by initializing memory to the program's values.
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A position in memory is called an address (for example, the first value in
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memory is at "address 0").
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Opcodes (like 1, 2, or 99) mark the beginning of an instruction. The values
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used immediately after an opcode, if any, are called the instruction's
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parameters. For example, in the instruction 1,2,3,4, 1 is the opcode; 2, 3,
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and 4 are the parameters. The instruction 99 contains only an opcode and has
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no parameters.
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The address of the current instruction is called the instruction pointer; it
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starts at 0. After an instruction finishes, the instruction pointer
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increases by the number of values in the instruction; until you add more
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instructions to the computer, this is always 4 (1 opcode + 3 parameters) for
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the add and multiply instructions. (The halt instruction would increase the
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instruction pointer by 1, but it halts the program instead.)
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"With terminology out of the way, we're ready to proceed. To complete the
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gravity assist, you need to determine what pair of inputs produces the
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output 19690720."
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The inputs should still be provided to the program by replacing the values
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at addresses 1 and 2, just like before. In this program, the value placed in
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address 1 is called the noun, and the value placed in address 2 is called
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the verb. Each of the two input values will be between 0 and 99, inclusive.
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Once the program has halted, its output is available at address 0, also just
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like before. Each time you try a pair of inputs, make sure you first reset
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the computer's memory to the values in the program (your puzzle input) - in
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other words, don't reuse memory from a previous attempt.
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Find the input noun and verb that cause the program to produce the output
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19690720. What is 100 * noun + verb? (For example, if noun=12 and verb=2,
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the answer would be 1202.)
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Your puzzle answer was 5335.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should return to your Advent calendar and try another
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puzzle.
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If you still want to see it, you can get your puzzle input.
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You can also [Shareon Twitter Mastodon] this puzzle.
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References
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Visible links . https://adventofcode.com/ .
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https://adventofcode.com/2019/about . https://adventofcode.com/2019/events .
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https://adventofcode.com/2019/settings .
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https://adventofcode.com/2019/auth/logout . Advent of Code Supporter
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https://adventofcode.com/2019/support . https://adventofcode.com/2019 .
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https://adventofcode.com/2019 . https://adventofcode.com/2019/support .
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https://adventofcode.com/2019/sponsors .
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https://adventofcode.com/2019/leaderboard .
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https://adventofcode.com/2019/stats . https://adventofcode.com/2019/sponsors
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. https://www.hq.nasa.gov/alsj/a11/a11.landing.html#1023832 .
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https://en.wikipedia.org/wiki/Gravity_assist .
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https://en.wikipedia.org/wiki/Halt_and_Catch_Fire .
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https://en.wikipedia.org/wiki/Magic_smoke .
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https://en.wikipedia.org/wiki/Integer . https://adventofcode.com/2019 .
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https://adventofcode.com/2019/day/2/input
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