From ecc548a98719bfaea29b5669d6b7f5641678287a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20B=C3=BChler?= <stbuehler@web.de>
Date: Sat, 12 Dec 2020 11:21:28 +0100
Subject: [PATCH] day10

---
 data/day10/input | 104 +++++++++++++++++++++++++++++++++++++++++++++++
 src/bin/day10.rs |  39 ++++++++++++++++++
 2 files changed, 143 insertions(+)
 create mode 100644 data/day10/input
 create mode 100644 src/bin/day10.rs

diff --git a/data/day10/input b/data/day10/input
new file mode 100644
index 0000000..0815cd5
--- /dev/null
+++ b/data/day10/input
@@ -0,0 +1,104 @@
+79
+142
+139
+33
+56
+133
+138
+61
+125
+88
+158
+123
+65
+69
+105
+6
+81
+31
+60
+70
+159
+114
+71
+15
+13
+72
+118
+14
+9
+93
+162
+140
+165
+1
+80
+148
+32
+53
+102
+5
+68
+101
+111
+85
+45
+25
+16
+59
+131
+23
+91
+92
+115
+103
+166
+22
+145
+161
+108
+155
+135
+55
+86
+34
+37
+78
+28
+75
+7
+104
+121
+24
+153
+167
+95
+87
+94
+134
+154
+84
+151
+124
+62
+49
+38
+39
+54
+109
+128
+19
+2
+98
+122
+132
+141
+168
+8
+160
+50
+42
+46
+110
+12
+152
diff --git a/src/bin/day10.rs b/src/bin/day10.rs
new file mode 100644
index 0000000..ea2d282
--- /dev/null
+++ b/src/bin/day10.rs
@@ -0,0 +1,39 @@
+const INPUT: &str = include_str!("../../data/day10/input");
+
+fn calc(input: &[u32], cache: &mut [Option<u64>], ndx: usize) -> u64 {
+	if let Some(n) = cache[ndx] {
+		n
+	} else {
+		let cur = input[ndx];
+		let mut n = 0;
+		for next in ndx+1..input.len() {
+			if input[next] - cur > 3 { break; }
+			n += calc(input, cache, next);
+		}
+		cache[ndx] = Some(n);
+		n
+	}
+}
+
+fn main() {
+	let mut input: Vec<u32> = INPUT.lines().map(|s| s.parse().unwrap()).collect();
+	input.sort();
+
+	let mut prev = 0;
+	let mut count = [0, 0, 0];
+	{
+		for &j in &input {
+			count[(j - prev - 1) as usize] += 1;
+			prev = j;
+		}
+	}
+	count[2] += 1; // device always has diff of 3.
+	println!("#(joltage diff 1) * #(joltage diff 3): {}", count[2] * count[0]);
+
+	// insert outlet as first element
+	input.insert(0, 0);
+	let mut cache: Vec<Option<u64>> = input.iter().map(|_| None).collect();
+	cache[input.len()-1] = Some(1); // always need last adapter
+
+	println!("Combinations: {}", calc(&input, &mut cache, 0));
+}