Discussion on: AoC Day 21: Chronal Conversion

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JavaScript solution

My case was exactly the same as @jmgimeno , I used the same analyzer from day 19 and I came down to the same conclusions as him:

for part 1, the solution is the first time the code reaches the check if register[5] is the same as register0
for part 2, I decided that I had to check for loops and the last solution before the 1st loop is the solution.

As usual, I'm gonna omit reader.js which is the same as the other solutions and jump to the point:

21a.js

const { readFile } = require('./reader');
const {
    operations
} = require('./16-common');
const {
    readInput,
    analyzeProgram
} = require ('./19-common');

const runProgram = (ipRegister, program) => {
    let registers = [0, 0, 0, 0, 0, 0];
    const n = program.length;
    let ip = registers[ipRegister];
    while (ip >= 0 && ip < n) {
        const instruction = program[ip];
        const op = operations[instruction[0]];
        registers = op(instruction)(registers);
        ip = ++registers[ipRegister];
        if (ip === 28) {            
            return registers[5];
        }
    }

    return registers[5];
};

(async () => {
    const lines = await readFile('21-input.txt');

    const { ipRegister, program } = readInput(lines);

    //analyzeProgram(ipRegister, program);

    const solution = runProgram(ipRegister, program);

    console.log(`The lowest non-negative integer value for register 0 that causes the program to halt after executing the fewest instructions is ${solution}.`);
})();

21b.js

const { readFile } = require('./reader');
const {
    operations
} = require('./16-common');
const {
    readInput,
    analyzeProgram
} = require ('./19-common');

const runProgram = (ipRegister, program) => {
    let registers = [0, 0, 0, 0, 0, 0];
    const n = program.length;
    let ip = registers[ipRegister];
    const frequency = new Set();
    let lastSolution;
    while (ip >= 0 && ip < n) {
        const instruction = program[ip];
        const op = operations[instruction[0]];
        registers = op(instruction)(registers);
        ip = ++registers[ipRegister];
        if (ip === 28) {            
            if (frequency.has(registers[5])) {
                return lastSolution;
            }
            else  {
                lastSolution = registers[5];
                frequency.add(lastSolution);
            }
        }
    }

    return registers[5];
};

(async () => {
    const lines = await readFile('21-input.txt');

    const { ipRegister, program } = readInput(lines);

    //analyzeProgram(ipRegister, program);

    const solution = runProgram(ipRegister, program);

    console.log(`The lowest non-negative integer value for register 0 that causes the program to halt after executing the most instructions is ${solution}.`);
})();