Advent of Code 2020 - Day 5 Binary Boarding

day05_binary_boarding.cpp

#include <iostream>
#include <string>
#include <queue>
using namespace std;

int process(string&);

int main() {
    string pass;
    priority_queue<int> ids;
    while(getline(cin, pass)) {
        ids.push(process(pass));
    }
    // part 1
    cout << "Part 1: " << ids.top() << "\n";

    // part 2
    int last = ids.top();
    while (!ids.empty()) {
        ids.pop();
        if (ids.top() != last-1){
            cout << "Part 2: " << last-1 << "\n";
            break;
        }
        last = ids.top();
    }
    return 0;
}

short search(string &str, short upper, short n, char left){
    short lower=0, mid;
    for(short i=0; i<=n; i++) {
        mid = (lower + upper) / 2;
        if (str[i] == left) upper = mid;
        else lower = mid+1;
    }
    return mid;
}

int process(string &pass){
    short row, col;
    row = search(pass, 127, 7, 'F');

    string column = pass.substr(7);
    col = search(column, 7, 3, 'L');
    return row*8 + col;
}