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Commit4329c24

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day 14 part 2; add notes to journal
1 parent57a3cdf commit4329c24

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4 files changed

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‎README.md‎

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@@ -125,3 +125,22 @@ Day 23 was one of those problems where I took an entirely different approach in
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Usually when this happens, I "align" the two solutions so they re-use the same code. I started to do that
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after finishing part 2 but the approaches are so algorithmically different that I decided it wasn't worth
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the energy.
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(time passes)
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Well, I've finished a solid pass through all the problems. Here's what I need to return to:
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```
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Day 14 part 2 = finding the christmas tree
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Day 17 part 2 = [quine](https://en.wikipedia.org/wiki/Quine_(computing))-ish problem
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Day 21 part 2 = keypad problem
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Day 24 part 2 = find 4 swaps of logic gates to make addition work
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```
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I think I can do 14 and 21, if I put my mind to it. Honestly, I'm not sure about the other two.
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For those, I may ask my friend Rob who's also doing AoC this year, or look at reddit, instead of beating my
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head against a wall. Which I did for WEEKS for some problems during AoC 2018. Which was not healthy.
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(more time passes)
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Hey I figured out day 14!
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packagecom.codefork.aoc2024.day14;
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importcom.codefork.aoc2024.Problem;
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importjava.util.stream.Stream;
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publicclassPart02extendsProblem {
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publicStringsolve(intwidth,intheight,Stream<String>data) {
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// I tried a bunch of different strategies, including looking for unbalanced robot
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// counts in different quadrants, thinking that the quadrant stuff in part 1 was a hint.
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// I couldn't get that to work. after stepping away from it for over a week,
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// I thought to try a different approach: just look for clusters of adjacent robots,
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// since a picture is likely to have such clusters. at a low threshold, it displayed
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// a few false positives before yielding the answer, so it was just a matter of increasing
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// the threshold to something reasonable once I knew what the Christmas tree actually looked like.
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System.out.println("This takes ~40 seconds");
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varswarm =Swarm.create(data,width,height);
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varkeepGoing =true;
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vari =0;
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while(keepGoing) {
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varnewSwarm =swarm.doMoves(1);
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varadjacentClusters =newSwarm.getAdjacentClusters();
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varhasLines =adjacentClusters.stream().anyMatch(cluster ->
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cluster.size() >20);
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if(hasLines) {
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newSwarm.print();
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keepGoing =false;
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}else {
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swarm =newSwarm;
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i++;
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}
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}
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returnString.valueOf(i+1);
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}
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@Override
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publicStringsolve() {
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returnsolve(101,103,getInput());
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}
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publicstaticvoidmain(String[]args) {
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newPart02().run();
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}
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}

‎src/main/java/com/codefork/aoc2024/day14/Part02.java.bak‎

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This file was deleted.

‎src/main/java/com/codefork/aoc2024/day14/Swarm.java‎

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importcom.codefork.aoc2024.util.Maps;
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importjava.util.ArrayList;
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importjava.util.HashSet;
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importjava.util.List;
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importjava.util.Map;
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importjava.util.Set;
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importjava.util.regex.Pattern;
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importjava.util.stream.Collectors;
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importjava.util.stream.IntStream;
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publicrecordSwarm(List<Robot>robots,intwidth,intheight) {
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publicrecordPosition(intx,inty) {
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publicbooleanisAdjacent(Positionother) {
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varxDiff =Math.abs(other.x() -x);
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varyDiff =Math.abs(other.y() -y);
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returnxDiff +yDiff <=1;
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}
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}
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publicrecordVelocity(intdx,intdy) {
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));
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}
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/**
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* testing for part 2: try smaller sections
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*/
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publicMap<Integer,Integer>getCustomSectionCounts() {
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varbyQuadrant =robots.stream()
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.collect(Collectors.groupingBy(
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(robot) -> {
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if (robot.position().y() <height /3) {
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if (robot.position().x() <width /2) {
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return0;
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}elseif (robot.position().x() >width /2) {
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return1;
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}
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}elseif (robot.position().y() >height /3 &&robot.position().y() < (height /3) *2) {
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if (robot.position().x() <width /2) {
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return2;
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}elseif (robot.position().x() >width /2) {
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return3;
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}
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}elseif (robot.position().y() > (height /3) *2) {
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if (robot.position().x() <width /2) {
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return4;
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}elseif (robot.position().x() >width /2) {
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return5;
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}
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}
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// put the robots on the center lines in a separate group
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// that we'll discard
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returnDISCARD;
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})
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);
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returnbyQuadrant.entrySet().stream()
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.filter(entry ->entry.getKey() !=DISCARD)
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.collect(Collectors.toMap(
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Map.Entry::getKey,
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entry -> {
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// count occupied positions rather than robots, since they can be stacked, and we only
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// care about what they look like from above
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recordPos(intx,inty) {
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}
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varlist =entry.getValue();
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varoccupiedPositions =list.stream()
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.map(robot ->newPos(robot.position().x(),robot.position().y()))
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.collect(Collectors.toSet());
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returnoccupiedPositions.size();
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},
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Integer::sum
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));
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}
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publicintgetSafetyFactor() {
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returngetQuadrantCounts().entrySet().stream()
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.reduce(1, (acc,entry) ->acc *entry.getValue(),Integer::sum);
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}
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/**
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* Look for groups of adjacent robots. this returns a list of sets of positions, not
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* the Robots themselves, because we only care about positions. We actually only care about the
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* existence of clusters, not even the positions.
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*/
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publicList<Set<Position>>getAdjacentClusters() {
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varclusters =newArrayList<Set<Position>>();
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for(varrobot :robots()) {
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varposition =robot.position();
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varnewClusters =newArrayList<Set<Swarm.Position>>();
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varmergedCluster =newHashSet<Position>();
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for(varcluster :clusters) {
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varbelongs =cluster.stream().anyMatch(p ->p.isAdjacent(position));
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if(belongs) {
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mergedCluster.addAll(cluster);
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mergedCluster.add(position);
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}else {
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newClusters.add(cluster);
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}
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}
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if(mergedCluster.isEmpty()) {
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mergedCluster.add(position);
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}
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newClusters.add(mergedCluster);
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clusters =newClusters;
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}
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returnclusters;
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}
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}

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