Added day3

inputs/sample.txt

@@ -0,0 +1,12 @@
+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010

src/bin/day3.rs

@@ -0,0 +1,105 @@
+use std::error::Error;
+use std::fs::File;
+use std::io::{self, BufRead};
+use std::vec::Vec;
+
+const word_len: usize = 12;
+
+fn to_weights(line: String) -> Vec<i32> {
+    let mut result = zero_fill(word_len);
+    for i in 0..word_len {
+        result[i] = match line.chars().nth(i) {
+            Some('1') => 1,
+            Some('0') => -1,
+            _ => panic!("Line to short"),
+        };
+    }
+
+    result
+}
+
+fn sum_weights(acc: Vec<i32>, weights: &Vec<i32>) -> Vec<i32> {
+    acc.iter().zip(weights.iter()).map(|(a, b)| a + b).collect()
+}
+
+fn zero_fill(len: usize) -> Vec<i32> {
+    let mut res = Vec::<i32>::new();
+    res.resize(len, 0);
+    res
+}
+
+fn weights_to_int(weights: &Vec<i32>) -> i32 {
+    let mut res = 0;
+    for i in 0..weights.len() {
+        if weights[i] > 0 {
+            res |= 1 << word_len - 1 - i;
+        }
+    }
+    res
+}
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let file = File::open("inputs/day3.txt")?;
+    let lines = io::BufReader::new(file).lines().map(|l| l.unwrap());
+
+    let weights: Vec<Vec<i32>> = lines.map(|l| to_weights(l)).collect();
+
+    let bits: Vec<i32> = weights.iter().fold(zero_fill(word_len), sum_weights);
+
+    let mut gamma = 0;
+    let mut epsilon = 0;
+
+    for i in 0..bits.len() {
+        if bits[i] > 0 {
+            gamma |= 1 << word_len - 1 - i;
+        } else {
+            epsilon |= 1 << word_len - 1 - i;
+        }
+    }
+
+    println!("Gamma: {}", gamma);
+    println!("epsilon: {}", epsilon);
+
+    println!("Answer1: {}", gamma * epsilon);
+
+    let mut selection_pos = 0;
+    let mut oxy_weights = weights.clone();
+    let mut oxy_bits = bits.clone();
+    while oxy_weights.len() > 1 {
+        oxy_weights = oxy_weights
+            .into_iter()
+            .filter(|weights| {
+                (weights[selection_pos] == 1 && oxy_bits[selection_pos] > 0)
+                    || (weights[selection_pos] == -1 && oxy_bits[selection_pos] < 0)
+                    || (weights[selection_pos] == 1 && oxy_bits[selection_pos] == 0)
+            })
+            .collect();
+        selection_pos += 1;
+        oxy_bits = oxy_weights.iter().fold(zero_fill(word_len), sum_weights);
+    }
+    println!("oxy_weights: {:?}", oxy_weights);
+
+    selection_pos = 0;
+    let mut co2_weights = weights.clone();
+    let mut co2_bits = bits.clone();
+    while co2_weights.len() > 1 {
+        co2_weights = co2_weights
+            .into_iter()
+            .filter(|weights| {
+                (weights[selection_pos] == -1 && co2_bits[selection_pos] > 0)
+                    || (weights[selection_pos] == 1 && co2_bits[selection_pos] < 0)
+                    || (weights[selection_pos] == -1 && co2_bits[selection_pos] == 0)
+            })
+            .collect();
+        selection_pos += 1;
+        co2_bits = co2_weights.iter().fold(zero_fill(word_len), sum_weights);
+    }
+    println!("co2_weights: {:?}", co2_weights);
+
+    let oxy = weights_to_int(&oxy_weights[0]);
+    let co2 = weights_to_int(&co2_weights[0]);
+
+    println!("Answer2: {}", oxy * co2);
+
+    Ok(())
+}