AoC22/d03.cc

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

using namespace std;

typedef vector<vector<unsigned char>> Input;

Input parse()
{
    Input items;
    for (string line; getline(cin, line);) {
        vector<unsigned char> bag;
        for (unsigned char c : line) {
            if (c >= 'a') c = c - 'a' + 1;
            else if (c >= 'A') c = c - 'A' + 27;
            bag.push_back(c);
        }
        items.push_back(bag);
    }
    return items;
}

template<class T>
unordered_set<T> intersect(unordered_set<T> &a, unordered_set<T> &b)
{
    unordered_set<T> o;
    copy_if(a.begin(), a.end(), inserter(o, o.end()), [&](T i){return b.count(i);});
    return o;
}

unsigned p1(Input &items)
{
    unsigned sum = 0;
    for (auto i : items) {
        unsigned len = i.size() / 2;
        auto one = unordered_set<unsigned char>(i.begin(), i.begin() + len);
        auto two = unordered_set<unsigned char>(i.begin() + len, i.begin() + len * 2);
        for (auto x : intersect(one, two)) sum += x;
    }
    return sum;
}

unsigned p2(Input &items)
{
    unsigned sum = 0;
    for (auto i = items.begin(); i < items.end(); i += 3) {
        auto one = unordered_set<unsigned char>(i[0].begin(), i[0].end());
        auto two = unordered_set<unsigned char>(i[1].begin(), i[1].end());
        auto thr = unordered_set<unsigned char>(i[2].begin(), i[2].end());
        auto inter = intersect(one, two);
        inter = intersect(inter, thr);
        for (auto x : inter) sum += x;
    }
    return sum;
}

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