From fc6bff03e09191af164f6cc9e6e016db6f91fd44 Mon Sep 17 00:00:00 2001
From: Christopher Bohn <bohn@unl.edu>
Date: Fri, 9 Dec 2022 09:51:20 -0600
Subject: [PATCH] Completed Year 2022 Day 9 part 1
---
2022/README.md | 7 +-
.../java/edu/unl/cse/bohn/year2022/Day9.java | 100 ++++++++++++++++++
2 files changed, 106 insertions(+), 1 deletion(-)
create mode 100644 2022/src/main/java/edu/unl/cse/bohn/year2022/Day9.java
diff --git a/2022/README.md b/2022/README.md
index b0c0ae5..6f32678 100644
--- a/2022/README.md
+++ b/2022/README.md
@@ -258,7 +258,12 @@ Well... I'm going to take the part 2 code in a (very) slightly different directi
### Part 1
The subproblems are
-- ...
+- Determine whether the head and tail are touching
+- Determine what direction the tail should move
+- Both of the previous subproblems include the subproblem of finding the distance between the head and tail along each
+ dimension
+- Track which locations the tail has visited
+- Count those locations
### Part 2
diff --git a/2022/src/main/java/edu/unl/cse/bohn/year2022/Day9.java b/2022/src/main/java/edu/unl/cse/bohn/year2022/Day9.java
new file mode 100644
index 0000000..ecb6ad8
--- /dev/null
+++ b/2022/src/main/java/edu/unl/cse/bohn/year2022/Day9.java
@@ -0,0 +1,100 @@
+package edu.unl.cse.bohn.year2022;
+
+import edu.unl.cse.bohn.Puzzle;
+
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.stream.IntStream;
+
+@SuppressWarnings("unused")
+public class Day9 extends Puzzle {
+ public Day9(boolean isProductionReady) {
+ super(isProductionReady);
+ sampleData = """
+ R 4
+ U 4
+ L 3
+ D 1
+ R 4
+ D 1
+ L 5
+ R 2""";
+ }
+
+ @Override
+ public long computePart1(List<String> data) {
+ List<Character> movements = extractIndividualMovements(data);
+ int totalDistanceTravelled = movements.size();
+ boolean[][] visitedLocations = new boolean[2 * totalDistanceTravelled][2 * totalDistanceTravelled];
+ Arrays.stream(visitedLocations).forEach(row -> Arrays.fill(row, false));
+ Position head = new Position(totalDistanceTravelled, totalDistanceTravelled);
+ Position tail = new Position(totalDistanceTravelled, totalDistanceTravelled);
+ visitedLocations[tail.row][tail.column] = true;
+ for (Character movement : movements) {
+ head = switch (movement) {
+ case 'R' -> new Position(head.row, head.column + 1);
+ case 'L' -> new Position(head.row, head.column - 1);
+ case 'U' -> new Position(head.row + 1, head.column);
+ case 'D' -> new Position(head.row - 1, head.column);
+ default -> throw new IllegalStateException("Unrecognized movement: " + movement);
+ };
+ tail = tail.moveToward(head);
+ visitedLocations[tail.row][tail.column] = true;
+ }
+ return countVisitedLocations(visitedLocations);
+ }
+
+ @Override
+ public long computePart2(List<String> data) {
+ return 0;
+ }
+
+ private record Position(int row, int column) {
+ public Position moveToward(Position destination) {
+ int rowDifference = destination.row - this.row;
+ int columnDifference = destination.column - this.column;
+ if (Math.abs(rowDifference) <= 1 && Math.abs(columnDifference) <= 1) {
+ return this;
+ } else if (rowDifference == 0) {
+ return new Position(row, (columnDifference > 0) ? column + 1 : column - 1);
+ } else if (columnDifference == 0) {
+ return new Position((rowDifference > 0) ? row + 1 : row - 1, column);
+ } else {
+ return new Position(
+ (rowDifference > 0) ? row + 1 : row - 1,
+ (columnDifference > 0) ? column + 1 : column - 1
+ );
+ }
+ }
+ }
+
+ private List<Character> extractIndividualMovements(List<String> data) {
+ List<Character> movements = new LinkedList<>();
+ for (String datum : data) {
+ char direction = datum.charAt(0);
+ int distance = Integer.parseInt(datum.substring(2));
+ IntStream.range(0, distance).mapToObj(i -> direction).forEach(movements::add);
+ }
+ return movements;
+ }
+
+ private long countVisitedLocations(boolean[][] visitedLocations) {
+ int numberOfVisitedLocations = 0;
+ for (boolean[] visitedRow : visitedLocations) {
+ for (boolean visitedLocation : visitedRow) {
+ numberOfVisitedLocations += visitedLocation ? 1 : 0;
+ }
+ }
+ return numberOfVisitedLocations;
+ }
+
+ private void printLocations(boolean[][] locations) {
+ for (boolean[] row : locations) {
+ for (boolean location : row) {
+ System.out.print(location ? '#' : '.');
+ }
+ System.out.println();
+ }
+ }
+}
--
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