Day 2 part 1

day_02/src/main.rs

@@ -1,3 +1,82 @@
-fn main() {
+use std::collections::HashMap;
-    println!("Hello, world!");
+use std::env;
+use std::error::Error;
+use std::fs::File;
+use std::io::{BufReader, prelude::*};
+use std::str::FromStr;
+
+/// Parse a report into a Vec<T>
+fn parse_report<T>(line: &str) -> Result<Vec<T>, <T as FromStr>::Err>
+where
+    T: FromStr,
+{
+    let parsed_line = line
+        .split(char::is_whitespace)
+        .map(|v| v.parse())
+        .collect::<Result<Vec<T>, _>>()?;
+    Ok(parsed_line)
+}
+
+enum ReportDirection {
+    Asc,
+    Desc,
+}
+
+fn is_report_safe(report: &Vec<i64>) -> bool {
+    let direction = if report[0] < report[1] {
+        ReportDirection::Asc
+    } else {
+        ReportDirection::Desc
+    };
+
+    match direction {
+        ReportDirection::Asc => {
+            let mut prev_report_level = report[0];
+            for report_level in report[1..].iter() {
+                if prev_report_level >= *report_level || report_level - prev_report_level > 3 {
+                    return false;
+                }
+                prev_report_level = *report_level;
+            }
+        }
+        ReportDirection::Desc => {
+            let mut prev_report_level = report[0];
+            for report_level in report[1..].iter() {
+                if prev_report_level <= *report_level || prev_report_level - report_level > 3 {
+                    return false;
+                }
+                prev_report_level = *report_level;
+            }
+        }
+    };
+
+    true
+}
+
+fn main() -> Result<(), Box<dyn Error>> {
+    // Handle command input
+    let args: Vec<String> = env::args().collect();
+    if args.len() != 2 {
+        panic!(
+            "{} must be run with a single argument of files name!",
+            &args[0]
+        )
+    }
+    let input_file_string = &args[1];
+
+    let input_file = File::open(input_file_string)?;
+    let input_reader = BufReader::new(input_file);
+
+    let mut accumulator = 0;
+    for line in input_reader.lines() {
+        let line = line?;
+        let parsed_report: Vec<i64> = parse_report(&line)?;
+        if is_report_safe(&parsed_report) {
+            accumulator += 1;
+        }
+    }
+
+    println!("Number of SAFE reports: {}", accumulator);
+
+    Ok(())
 }