AoC2021 Problem 7

problem7ab.cpp

#include <fstream>
#include <string>
#include <sstream>
#include <iostream>
#include <vector>
#include <numeric>

using namespace std;

template <typename T>
vector<T> line2vec(string line, char sep = ',')
{
    vector<T> arr;
    stringstream ss(line);

    for (T i; ss >> i;)
    {
        arr.push_back(i);
        while (ss.peek() == sep)
            ss.ignore();
    }

    return arr;
}

int main(int argc, char *argv[])
{
    std::ifstream fin;
    string line;
    vector<int> crabs;
    long totalEnergy = 0;
    std::function<int(int)> arithSum = [=](int dist) -> float
    { return dist * (dist + 1) / 2; };

    // Read the input and populate the population
    fin.open(argv[1], std::ios_base::in);
    getline(fin, line);
    crabs = line2vec<int>(line, ',');

    //  Find the median value
    sort(crabs.begin(), crabs.end());
    int n = crabs.size();
    double moveTo = (double)(crabs[(n - 1) / 2] + crabs[n / 2]) / 2.0;

    // Part 1

    for (int c : crabs)
    {
        totalEnergy += abs(moveTo - c);
    }

    cout << "Total Energy: " << totalEnergy << endl;

    // Part 2
    moveTo = std::accumulate(crabs.begin(), crabs.end(), decltype(crabs)::value_type(0));
    moveTo /= double(crabs.size());
    int moveToDisc_ceil = static_cast<int>(ceil(moveTo));
    int moveToDisc_floor = static_cast<int>(floor(moveTo));

    int totalEnergy_up = 0;
    int totalEnergy_down = 0;
    for (int c : crabs)
    {
        totalEnergy_up += arithSum(abs(moveToDisc_ceil - c));
        totalEnergy_down += arithSum(abs(moveToDisc_floor - c));
    }
    totalEnergy = min(totalEnergy_up, totalEnergy_down);

    cout
        << "Part2: " << totalEnergy << endl;

    return 0;
}