Day5.java

package com.sbaars.adventofcode.year20.days;

import com.sbaars.adventofcode.year20.Day2020;

import java.util.HashSet;
import java.util.Set;

public class Day5 extends Day2020 {

  public Day5() {
    super(5);
  }

  public static void main(String[] args) {
    new Day5().printParts();
  }

  @Override
  public Object part1() {
    return getSeatIds(dayStrings()).stream().mapToInt(e -> e).max().getAsInt();
  }

  private Set<Integer> getSeatIds(String[] boardingPasses) {
    Set<Integer> l = new HashSet<>();
    for (String s : boardingPasses) {
      int rowLow = 0;
      int rowHigh = 127;
      int columnLow = 0;
      int columnHigh = 7;
      for (char c : s.toCharArray()) {
        if (c == 'F') {
          rowHigh -= (rowHigh - rowLow + 1) / 2;
        } else if (c == 'B') {
          rowLow += (rowHigh - rowLow + 1) / 2;
        } else if (c == 'L') {
          columnHigh -= (columnHigh - columnLow + 1) / 2;
        } else if (c == 'R') {
          columnLow += (columnHigh - columnLow + 1) / 2;
        }
      }
      l.add(rowHigh * 8 + columnHigh);
    }
    return l;
  }

  @Override
  public Object part2() {
    Set<Integer> l = getSeatIds(dayStrings());
    return l.stream().mapToInt(e -> e).filter(n -> l.contains(n) && l.contains(n + 2) && !l.contains(n + 1)).sum() + 1;
  }
}