From 4a8c1d460df08d963059753e84d33067d8bb96b2 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Fri, 3 Dec 2021 04:59:44 -0400
Subject: [PATCH] feat: complete day 3

---
 rust/2021/src/day_03.rs | 61 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 54 insertions(+), 7 deletions(-)

diff --git a/rust/2021/src/day_03.rs b/rust/2021/src/day_03.rs
index 9c4c1ee..7e8639f 100644
--- a/rust/2021/src/day_03.rs
+++ b/rust/2021/src/day_03.rs
@@ -1,9 +1,55 @@
-fn solve_part1(input: &str) -> i32 {
-    todo!();
+fn solve_part1(input: &str) -> u32 {
+    let (report, bit_len) = parse_input(input);
+    let mut gamma: u32 = 0;
+
+    for i in 0..bit_len {
+        let count = report.iter().filter(|v| **v >> i & 0x01 == 0x01).count();
+
+        if count > report.len() - count {
+            gamma |= 1 << i
+        } else {
+            gamma &= !(1 << i)
+        }
+    }
+
+    gamma * (!gamma & ((1 << bit_len) - 1))
 }
 
-fn solve_part2(input: &str) -> i32 {
-    todo!();
+fn solve_part2(input: &str) -> u32 {
+    let (oxy_gen, bit_len) = parse_input(input);
+    let co2_gen = oxy_gen.clone();
+
+    let left = part2_logic(oxy_gen, bit_len, true);
+    let right = part2_logic(co2_gen, bit_len, false);
+
+    left * right
+}
+
+fn part2_logic(mut gen: Vec<u16>, bit_len: usize, is_oxy: bool) -> u32 {
+    for i in 0..bit_len {
+        if gen.len() < 2 {
+            break;
+        }
+
+        let count = gen
+            .iter()
+            .filter(|v| **v >> (bit_len - 1 - i) & 0x01 == 0x01)
+            .count();
+
+        let common = (count >= gen.len() - count) as u16;
+        let needle = if is_oxy { 1 - common } else { common };
+        gen.retain(|v| *v >> (bit_len - 1 - i) & 0x01 == needle);
+    }
+
+    gen[0] as u32
+}
+
+fn parse_input(input: &str) -> (Vec<u16>, usize) {
+    let mut it = input.lines().peekable();
+    let size = it.peek().expect("1 > &str exists").len();
+    let report = it.flat_map(|s| u16::from_str_radix(s, 2).ok()).collect();
+
+    (report, size)
 }
 
 pub fn run(input: String) {
@@ -16,15 +62,16 @@ pub fn run(input: String) {
 
 #[cfg(test)]
 mod tests {
-    const EXAMPLE_INPUT: &str = todo!();
+    const EXAMPLE_INPUT: &str =
+        "00100\n11110\n10110\n10111\n10101\n01111\n00111\n11100\n10000\n11001\n00010\n01010";
 
     #[test]
     fn part1() {
-        todo!();
+        assert_eq!(super::solve_part1(EXAMPLE_INPUT), 198);
     }
 
     #[test]
     fn part2() {
-        todo!();
+        assert_eq!(super::solve_part2(EXAMPLE_INPUT), 230);
     }
 }