AoC22/d10.cc

#include <iostream>
#include <vector>

using namespace std;

enum Opcode {
    NOOP,
    ADDX
};

struct Instr {
    Opcode op;
    int arg;
};

unsigned instr_cycles[] = {
    1,  // NOOP
    2   // ADDX
};

typedef vector<Instr> Input;

Input parse()
{
    Input data;
    for (string line; getline(cin, line);) {
        Instr instr;
        string op = line.substr(0, 5);
        if (op == "noop") {
            instr.op = NOOP;
        } else if (op == "addx ") {
            instr.op = ADDX;
            instr.arg = stoi(line.substr(5));
        }
        data.push_back(instr);
    }
    return data;
}

class Cpu {
    const vector<Instr> *prog;
    vector<Instr>::const_iterator cur;
    unsigned cur_cycles = 0;
    bool run = true;

public:
    unsigned cycle = 1;
    int X = 1;

    Cpu(const vector<Instr> *prog) {
        this->prog = prog;
        this->cur = prog->begin();
    }

    void tick();
    bool running() { return run; }
};

void Cpu::tick()
{
    if (!run) return;

    // Fetch next instruction
    if (!cur_cycles) {
        cur_cycles = instr_cycles[cur->op];
    }

    // Execute instruction when done
    if (!--cur_cycles) {
        switch (cur->op) {
        case NOOP:
            break;

        case ADDX:
            this->X += cur->arg;
            break;
        }
        cur++;
        if (cur >= prog->end()) run = false;
    }

    cycle++;
}

unsigned p1(const Input &input)
{
    unsigned sum = 0;
    Cpu cpu(&input);
    while (cpu.running()) {
        if ((cpu.cycle + 20) % 40 == 0) sum += cpu.cycle * cpu.X;
        cpu.tick();
    }
    return sum;
}

void p2(const Input &input)
{
    Cpu cpu(&input);
    while (cpu.running()) {
        // Calculate current CRT line
        int X = cpu.cycle % 40;
        if (X == 0) X += 40;

        // Draw pixel
        if (cpu.X <= X && X <= cpu.X + 2) cout << '#';
        else cout << '.';
        if (X == 40) cout << endl;

        cpu.tick();
    }
}

int main()
{
    auto input = parse();
    cout << p1(input) << endl;
    p2(input);
}