From 3b877bf4cc667eb8bcc787d145203600a4dba2d2 Mon Sep 17 00:00:00 2001
From: Prefetch
Date: Sat, 25 Feb 2023 11:41:27 +0100
Subject: Initial commit

---
 d16/src/main.rs | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 d16/src/main.rs

(limited to 'd16/src')

diff --git a/d16/src/main.rs b/d16/src/main.rs
new file mode 100644
index 0000000..06ba9e1
--- /dev/null
+++ b/d16/src/main.rs
@@ -0,0 +1,81 @@
+fn generate_data(input: &str, length: usize) -> String {
+    let mut a = String::from(input);
+
+    while a.len() < length {
+        let mut b = String::new();
+
+        // Fill `b' with reversed and bit-flipped `a'
+        for c in a.chars().rev() {
+            b.push(if c == '0' { '1' } else { '0' });
+        }
+
+        a = format!("{}0{}", a, b);
+    }
+
+    a.truncate(length);
+    a
+}
+
+fn get_checksum(data: &str) -> String {
+    let mut chars: Vec<char> = data.chars().collect();
+
+    while chars.len() % 2 == 0 {
+        let mut next = Vec::new();
+
+        // For each pair of characters (length is even due to `while')
+        for i in 0..chars.len() / 2 {
+            // If both chars in this pair are equal
+            if chars[2 * i] == chars[2 * i + 1] {
+                next.push('1');
+            } else {
+                next.push('0');
+            }
+        }
+
+        chars = next;
+    }
+
+    chars.into_iter().collect()
+}
+
+fn solve_puzzle(input: &str, length: usize) -> String {
+    let data = generate_data(input, length);
+    get_checksum(&data)
+}
+
+fn main() {
+    // My personal puzzle input
+    let input = "11011110011011101";
+
+    // Part 1 gives 00000100100001100 for me
+    println!("Part 1 solution: {}", solve_puzzle(input, 272));
+
+    // Part 1 gives 00011010100010010 for me
+    println!("Part 2 solution: {}", solve_puzzle(input, 35651584));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_data() {
+        assert_eq!(generate_data("1", 3), "100");
+        assert_eq!(generate_data("0", 3), "001");
+        assert_eq!(generate_data("11111", 11), "11111000000");
+        assert_eq!(
+            generate_data("111100001010", 25),
+            "1111000010100101011110000"
+        );
+    }
+
+    #[test]
+    fn test_checksum() {
+        assert_eq!(get_checksum("110010110100"), "100");
+    }
+
+    #[test]
+    fn part1_example1() {
+        assert_eq!(solve_puzzle("10000", 20), "01100");
+    }
+}
-- 
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