aoc2024 d1

package aoc2024;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.junit.jupiter.api.Test;

import aoc2024.ak.Fn;
import aoc2024.ak.Parser;

public class D1 {

  @Test public void d1 () {
    List<Long> left = new ArrayList<>();
    List<Long> right = new ArrayList<>();
    { // build left and right list from text file
      List<String> lines = Fn.inputLinesTrimmed("d1.txt");
      for (String line : lines) {
        Parser p = new Parser(line);
        left.add(p.parseLong());
        p.eatAllWhitespace();
        right.add(p.parseLong());
      }
    }
    { // prepare for p1 (no effect on the outcome of p2)
      left.sort(Long::compare);
      right.sort(Long::compare);
    }
    { // p1
      long p1 = 0L;
      Fn.require(left.size() == right.size());
      for (int i = 0; i < left.size(); i++) {
        long l = left.get(i);
        long r = right.get(i);
        p1 += Math.abs(l - r);
      }
      System.out.println("p1: " + p1);
    }
    { // p2
      long p2 = 0L;
      for (Long l : left) {
        long rf = Collections.frequency(right, l);
        p2 += l * rf;
      }
      System.out.println("p2: " + p2);
    }
  }

}