Advent of Code 2020 - Day 12 Rain Risk

day12_rain_risk.cpp

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

using namespace std;

#define forn(i, j, n) for (int i = j; i < (int)n; i++)
#define forr(i, j, n) for (int i = j; i >= (int)n; i--)
#define fore(i, coll) for (auto i : coll)
#define endl '\n'
#define pb push_back
#define all(x) x.begin(), x.end()

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<string> vs;

int new_dir (vector<char> &, char, int);

int main() {
    // read inputs
    ifstream fin("inputs/12.txt");

    char act; short val;
    vector<pair<char, short>> inputs;
    while (fin >> act >> val) inputs.pb({act, val});

    // part 1
    vector<char> rights = {'N', 'E', 'S', 'W'};
    vector<char> lefts = {'N', 'W', 'S', 'E'};
    char curr='E';
    int x=0, y=0;
    for (auto &[action, value] : inputs) {
        if (action == 'F'){
            if (curr=='N') y+=value;
            if (curr=='S') y-=value;
            if (curr=='E') x+=value;
            if (curr=='W') x-=value;
        }
        else if (action=='N') y+=value;
        else if (action=='S') y-=value;
        else if (action=='E') x+=value;
        else if (action=='W') x-=value;
        else if (action=='R') curr = new_dir(rights, curr, value/90);
        else if (action=='L') curr = new_dir(lefts, curr, value/90);
    }
    cout << "Part 1: " << abs(x) + abs(y) << endl;

    // part 2
    curr='E';
    x=0, y=0;
    int wx=10, wy=1;
    for (auto &[action, value] : inputs) {
        if (action == 'F'){
            x += value*wx;
            y += value*wy;
        }
        else if (action=='N') wy+=value;
        else if (action=='S') wy-=value;
        else if (action=='E') wx+=value;
        else if (action=='W') wx-=value;
        else if (action=='R') {
            if (value == 90)  { swap(wx, wy); wy=-wy; }
            if (value == 180) { wx=-wx; wy=-wy; }
            if (value == 270) { swap(wx, wy); wx=-wx; }
        }
        else if (action=='L') {
            if (value == 90)  { swap(wx, wy); wx=-wx; }
            if (value == 180) { wx=-wx; wy=-wy; }
            if (value == 270) { swap(wx, wy); wy=-wy; }
        }
    }
    cout << "Part 2: " << abs(x) + abs(y) << endl;

    return 0;
}

int new_dir (vector<char> &dirs, char current, int moves){
    short curr_pos=-1;
    forn(i,0,4) if(dirs[i]==current) curr_pos=i;

    short facing_to = (curr_pos + moves) % 4;
    return dirs[facing_to];
}