From 000fb434a7f46a3b744dc20ea89b455364df9983 Mon Sep 17 00:00:00 2001
From: Christopher Bohn <bohn@unl.edu>
Date: Sun, 12 Dec 2021 09:30:36 -0600
Subject: [PATCH] Day 3 complete
---
2021/README.md | 7 +-
.../java/edu/unl/cse/bohn/year2021/Day3.java | 109 ++++++++++++++++++
2 files changed, 115 insertions(+), 1 deletion(-)
create mode 100644 2021/src/main/java/edu/unl/cse/bohn/year2021/Day3.java
diff --git a/2021/README.md b/2021/README.md
index eefe460..10d9f6a 100644
--- a/2021/README.md
+++ b/2021/README.md
@@ -9,4 +9,9 @@ get to use Java's new multiline strings.
Can we follow instructions? Yes we can. This isn't a particularly challenging
problem. Beside using Java's new Records, I'm also using Java's new style of
-switch statements.
\ No newline at end of file
+switch statements.
+
+## Day 3
+
+My CSCE 231 students should be able to do this problem in their sleep -- bit
+masks are cool.
\ No newline at end of file
diff --git a/2021/src/main/java/edu/unl/cse/bohn/year2021/Day3.java b/2021/src/main/java/edu/unl/cse/bohn/year2021/Day3.java
new file mode 100644
index 0000000..6bb074f
--- /dev/null
+++ b/2021/src/main/java/edu/unl/cse/bohn/year2021/Day3.java
@@ -0,0 +1,109 @@
+package edu.unl.cse.bohn.year2021;
+
+import edu.unl.cse.bohn.Puzzle;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BiPredicate;
+import java.util.stream.Collectors;
+
+@SuppressWarnings("unused")
+public class Day3 extends Puzzle {
+ private List<Integer> diagnosticReports;
+ private int reportLength;
+ private int[] ones, zeroes;
+
+ public Day3() {
+ day = 3;
+ sampleData = """
+ 00100
+ 11110
+ 10110
+ 10111
+ 10101
+ 01111
+ 00111
+ 11100
+ 10000
+ 11001
+ 00010
+ 01010""";
+ isProductionReady = true;
+ }
+
+ @Override
+ public int computePart1(List<String> data) {
+ diagnosticReports = data.stream().map(report -> Integer.parseInt(report, 2)).collect(Collectors.toList());
+ reportLength = data.get(0).length();
+ ones = new int[]{
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0};
+ zeroes = new int[]{
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0};
+ for (int report : diagnosticReports) {
+ for (int bit = 0; bit < reportLength; bit++) {
+ if ((report & (1 << bit)) == 0) {
+ zeroes[bit]++;
+ } else {
+ ones[bit]++;
+ }
+ }
+ }
+ int gamma = 0;
+ int epsilon = 0;
+ for (int bit = 0; bit < reportLength; bit++) {
+ if (ones[bit] > zeroes[bit]) {
+ gamma |= (1 << bit);
+ } else {
+ epsilon |= (1 << bit);
+ }
+ }
+ return gamma * epsilon;
+ }
+
+ private Integer filterReports(int[] onesArray, int[] zeroesArray, BiPredicate<Integer, Integer> predicate) {
+ List<Integer> workingSet = new ArrayList<>(diagnosticReports);
+ int bit = reportLength - 1;
+ int numberOfOnes = onesArray[bit];
+ int numberOfZeroes = zeroesArray[bit];
+ while (workingSet.size() > 1) {
+ int mask = 1 << bit;
+ if (predicate.test(numberOfOnes, numberOfZeroes)) {
+ workingSet = workingSet.stream()
+ .filter(report -> (report & mask) != 0)
+ .collect(Collectors.toList());
+ } else {
+ workingSet = workingSet.stream()
+ .filter(report -> (report & mask) == 0)
+ .collect(Collectors.toList());
+ }
+ bit--;
+ // Need to re-count the ones and zeroes since the old counts are now wrong
+ if (bit >= 0) {
+ numberOfOnes = numberOfZeroes = 0;
+ for (int report : workingSet) {
+ if ((report & (1 << bit)) == 0) {
+ numberOfZeroes++;
+ } else {
+ numberOfOnes++;
+ }
+ }
+ }
+ }
+ return workingSet.get(0);
+ }
+
+ @Override
+ public int computePart2(List<String> data) {
+ Integer oxygenGeneratorRating = filterReports(ones, zeroes,
+ (numberOfOnes, numberOfZeroes) -> numberOfOnes >= numberOfZeroes);
+ Integer co2ScrubberRating = filterReports(ones, zeroes,
+ (numberOfOnes, numberOfZeroes) -> numberOfOnes < numberOfZeroes);
+ return oxygenGeneratorRating * co2ScrubberRating;
+ }
+}
--
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