From 3711935b4f86128bf50d759e30b543766c738f13 Mon Sep 17 00:00:00 2001
From: Luke Hubmayer-Werner <mongoose41@gmail.com>
Date: Fri, 30 Dec 2022 20:06:01 +1030
Subject: [PATCH] Add Rust and C++ sliding XOR window versions of Day6

---
 2022/day6.cpp | 37 ++++++++++++++++++++++++++++++++++++-
 2022/day6.rs  | 36 +++++++++++++++++++++++++++++++++++-
 2 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/2022/day6.cpp b/2022/day6.cpp
index 3317947..d57c1e4 100644
--- a/2022/day6.cpp
+++ b/2022/day6.cpp
@@ -82,6 +82,40 @@ fourteen_found:
 	return std::pair<size_t, size_t>(four+2, fourteen+8);
 }
 
+
+std::pair<size_t, size_t> find_first_unique_runs_xor(std::vector<uint8_t> *s) {
+	size_t four = 0;
+	size_t fourteen = 0;
+	uint32_t masks[4096];
+	for (int i=0; i<4096; i++) {
+		masks[i] = 1 << ((*s)[i]-'a');
+	}
+	uint32_t bitset = 0;
+	for (int i = 0; i < 4; i++) {  // No old entries to remove
+		bitset ^= masks[i];
+	}
+	for (int i = 4; i < 4096; i++) {
+		bitset ^= masks[i];
+		bitset ^= masks[i-4];
+		if (std::popcount(bitset) >= 4) {
+			four = i;
+			break;
+		}
+	}
+	for (int i = four+1; i < four+11; i++) {  // No old entries to remove while readjusting base
+		bitset ^= masks[i];
+	}
+	for (int i = four+11; i < 4096; i++) {
+		bitset ^= masks[i];
+		bitset ^= masks[i-14];
+		if (std::popcount(bitset) >= 14) {
+			fourteen = i;
+			break;
+		}
+	}
+	return std::pair<size_t, size_t>(four, fourteen);
+}
+
 int main(int argc, char **argv) {
 	size_t iterations = 1000000;
 	auto filename = "input/6";
@@ -110,7 +144,8 @@ int main(int argc, char **argv) {
 	for (size_t i = 0; i<iterations; i++) {
 		// four = find_first_unique_run(&s, 4, 4);
 		// fourteen = find_first_unique_run(&s, 14, four);
-		auto result = find_first_unique_runs(&s);
+		// auto result = find_first_unique_runs(&s);
+		auto result = find_first_unique_runs_xor(&s);
 		four = result.first;
 		fourteen = result.second;
 	}
diff --git a/2022/day6.rs b/2022/day6.rs
index 8e1249e..740667a 100644
--- a/2022/day6.rs
+++ b/2022/day6.rs
@@ -87,6 +87,39 @@ fn find_first_unique_runs(s: &Vec<u8>) -> (Int, Int) {
 	return (four+4, fourteen+8);
 }
 
+fn find_first_unique_runs_xor(s: &Vec<u8>) -> (Int, Int) {
+	let mut four: Int = 0;
+	let mut fourteen: Int = 0;
+	let mut masks: [u32; 4096] = [0; 4096];
+	for i in 0..4096 {
+		masks[i] = 1 << (s[i]-b'a');
+	}
+	let mut bitset: u32 = 0;
+	for i in 0..4 {  // No old entries to remove
+		bitset ^= masks[i];
+	}
+	for i in 4..4096 {
+		bitset ^= masks[i];
+		bitset ^= masks[i-4];
+		if bitset.count_ones() >= 4 {
+			four = i;
+			break;
+		}
+	}
+	for i in (four+1)..(four+11) {  // No old entries to remove while readjusting base
+		bitset ^= masks[i];
+	}
+	for i in (four+11)..4096 {
+		bitset ^= masks[i];
+		bitset ^= masks[i-14];
+		if bitset.count_ones() >= 14 {
+			fourteen = i;
+			break;
+		}
+	}
+	return (four, fourteen);
+}
+
 fn main() {
 	let mut filename = "input/6";
 	let mut iterations = 1_000_000;
@@ -105,7 +138,8 @@ fn main() {
 	for _ in 0..iterations {
 		// four = find_first_unique_run(&s, 4, 0);
 		// fourteen = find_first_unique_run(&s, 14, four);
-		(four, fourteen) = find_first_unique_runs(&s);
+		// (four, fourteen) = find_first_unique_runs(&s);
+		(four, fourteen) = find_first_unique_runs_xor(&s);
 	}
 	let duration = t0.elapsed();
 	let per_iteration = duration / iterations;