AoC22/d05.cc

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

struct Instr {
    unsigned count;
    unsigned orig;
    unsigned dest;
};

struct Input {
    vector<vector<char>> stacks;
    vector<Instr> instrs;
};

vector<vector<char>> parse_stacks()
{
    vector<vector<char>> data;
    for (string line; getline(cin, line);) {
        if (line.empty()) break;
        unsigned count = (line.size() + 1) / 4;
        while (data.size() < count) data.resize(count);
        for (unsigned i = 0; i < count; i++) {
            auto pos = line.begin() + i * 4;
            if (pos[0] == '[' && pos[2] == ']') data[i].push_back(pos[1]);
        }
    }
    for (auto &x : data) reverse(x.begin(), x.end());
    return data;
}

vector<Instr> parse_instrs()
{
    vector<Instr> data;
    for (string line; getline(cin, line);) {
        Instr cur;
        sscanf(line.c_str(), "move %u from %u to %u",
                &cur.count, &cur.orig, &cur.dest);
        data.push_back(cur);
    }
    return data;
}

Input parse()
{
    Input data;
    data.stacks = parse_stacks();
    data.instrs = parse_instrs();
    return data;
}

string p1(const Input &input)
{
    auto stacks = input.stacks;
    for (auto &instr : input.instrs) {
        auto &o = stacks.at(instr.orig - 1);
        auto &d = stacks.at(instr.dest - 1);
        if (o.size() < instr.count) throw "instr error";
        for (unsigned i = 0; i < instr.count; i++) {
            d.push_back(o.back());
            o.pop_back();
        }
    }

    string out;
    for (auto &s : stacks) out.push_back(s.back());
    return out;
}

string p2(const Input &input)
{
    auto stacks = input.stacks;
    for (auto &instr : input.instrs) {
        auto &o = stacks.at(instr.orig - 1);
        auto &d = stacks.at(instr.dest - 1);
        if (o.size() < instr.count) throw "instr error";
        // std::copy maybe?
        for (unsigned i = 0; i < instr.count; i++) {
            d.push_back(*(o.end() - instr.count + i));
        }
        o.resize(o.size() - instr.count);
    }

    string out;
    for (auto &s : stacks) out.push_back(s.back());
    return out;
}

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