day3 part 1

day3/.gitignore

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+/target/

day3/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day3"
+version = "0.1.0"

day3/Cargo.toml

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+[package]
+name = "day3"
+version = "0.1.0"
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day3/src/main.rs

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+use std::{
+    fs::File,
+    io::{BufRead, BufReader, Lines, Result},
+    path::Path,
+};
+
+static INPUT_PATH: &str = "input.txt";
+
+fn main() -> Result<()> {
+    let diagnostic_report = read_diagnostic_report(INPUT_PATH)?;
+    let [gamma_rate, epsilon_rate] = extract_report_rates(&diagnostic_report);
+    println!("First puzzle: {}", gamma_rate * epsilon_rate);
+    Ok(())
+}
+
+fn extract_report_rates(report: &[String]) -> [i32; 2] {
+    let sums: Vec<i32> = report.iter().fold(vec![], |sums, curr| {
+        curr.chars()
+            .enumerate()
+            .map(|(index, char)| {
+                let value = if char == '0' { -1 } else { 1 };
+                sums.get(index).map_or(value, |sum| sum + value)
+            })
+            .collect()
+    });
+    let gamma_rate: String = sums
+        .iter()
+        .map(|&sum| if sum > 0 { "1" } else { "0" })
+        .collect::<Vec<&str>>()
+        .join("");
+    let epsilon_rate: String = sums
+        .iter()
+        .map(|&sum| if sum > 0 { "0" } else { "1" })
+        .collect::<Vec<&str>>()
+        .join("");
+    [
+        binary_str_to_int(&gamma_rate),
+        binary_str_to_int(&epsilon_rate),
+    ]
+}
+
+fn read_diagnostic_report(file_path: &str) -> Result<Vec<String>> {
+    read_lines(file_path).map(|lines| lines.filter_map(|line| line.ok()).collect())
+}
+
+fn binary_str_to_int(binary_str: &str) -> i32 {
+    i32::from_str_radix(binary_str, 2).unwrap()
+}
+
+// The output is wrapped in a Result to allow matching on errors
+// Returns an Iterator to the Reader of the lines of the file.
+fn read_lines<P>(filename: P) -> Result<Lines<BufReader<File>>>
+where
+    P: AsRef<Path>,
+{
+    let file = File::open(filename)?;
+    Ok(BufReader::new(file).lines())
+}

day3/test.txt

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+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010