star three

.gitignore

@@ -1,2 +1,3 @@
 /target
 /inputs
+/.vscode

src/main.rs

@@ -2,12 +2,14 @@ use std::env;
 
 mod star_one;
 mod star_two;
+mod star_three;
 
 fn main() {
     let args: Vec<String> = env::args().collect();
     match args[1].as_str() {
         "1" => star_one::run(),
         "2" => star_two::run(),
+        "3" => star_three::run(),
         _ => unreachable!(),
     }
 }

src/star_three.rs

@@ -0,0 +1,128 @@
+use std::fs;
+
+pub fn run() {
+    let file = fs::read_to_string("./inputs/star_three.txt").unwrap();
+    let input = file.lines();
+    let reports = parse_input(input);
+    let result = count_safe_reports(reports);
+    println!("Result: {}", result);
+}
+
+fn parse_input<'a, I>(str_lines: I) -> Vec<Vec<isize>>
+where
+    I: IntoIterator<Item = &'a str>
+{
+    let mut reports = vec![];
+
+    for str_line in str_lines {
+        let parsed_elems: Vec<isize> = str_line.split_whitespace().map(|n| n.to_string().parse::<isize>().unwrap()).collect();
+        reports.push(parsed_elems)
+    }
+
+    reports
+}
+
+fn count_safe_reports(reports: Vec<Vec<isize>>) -> usize {
+    reports.iter().filter(|&report| is_level_change_safe(report)).count()
+}
+
+#[derive(PartialEq, Copy, Clone)]
+enum Balancing {
+    Increasing,
+    Decreasing,
+}
+
+fn is_level_change_safe(report: &Vec<isize>) -> bool {
+    if report.len() < 2 {
+        return false;
+    }
+    let mut i = 1;
+    let mut last_balancing = None;
+    while i < report.len() {
+        let prev_level = report[i - 1];
+        let current_level = report[i];
+
+        if prev_level == current_level {
+            return false;
+        } 
+
+        let difference = match current_level > prev_level {
+            true => current_level - prev_level,
+            false => prev_level - current_level,
+        };
+
+        if difference > 3 {
+            return false;
+        }
+
+        if let Some(current_balancing) = last_balancing {
+            let new_balancing = match current_level > prev_level {
+                true => Balancing::Increasing,
+                false => Balancing::Decreasing,
+            };
+            if new_balancing != current_balancing {
+                return false;
+            }
+        } else {
+            last_balancing = match current_level > prev_level {
+                true => Some(Balancing::Increasing),
+                false => Some(Balancing::Decreasing),
+            }
+        }
+
+        i += 1;
+    }
+
+    true
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_input() {
+        let input = vec![
+            "7 6 4 2 1",
+            "1 2 7 8 9",
+            "9 7 6 2 1",
+            "1 3 2 4 5",
+            "8 6 4 4 1",
+            "1 3 6 7 9",
+        ];
+        let result = parse_input(input);
+        let expected_result = vec![
+            vec![7, 6, 4, 2, 1],
+            vec![1, 2, 7, 8, 9],
+            vec![9, 7, 6, 2, 1],
+            vec![1, 3, 2, 4, 5],
+            vec![8, 6, 4, 4, 1],
+            vec![1, 3, 6, 7, 9],
+        ];
+        assert_eq!(result, expected_result);
+    }
+
+    #[test]
+    fn test_count_safe_reports() {
+        let reports = vec![
+            vec![7, 6, 4, 2, 1],
+            vec![1, 2, 7, 8, 9],
+            vec![9, 7, 6, 2, 1],
+            vec![1, 3, 2, 4, 5],
+            vec![8, 6, 4, 4, 1],
+            vec![1, 3, 6, 7, 9],
+        ];
+        assert_eq!(count_safe_reports(reports), 2);
+    }
+
+    #[test]
+    fn test_is_level_change_safe() {
+        assert!(is_level_change_safe(&vec![7, 6, 4, 2, 1]));
+        assert!(!is_level_change_safe(&vec![1, 2, 7, 8, 9]));
+        assert!(!is_level_change_safe(&vec![9, 7, 6, 2, 1]));
+        assert!(!is_level_change_safe(&vec![1, 3, 2, 4, 5]));
+        assert!(!is_level_change_safe(&vec![8, 6, 4, 4, 1]));
+        assert!(is_level_change_safe(&vec![1, 3, 6, 7, 9]));
+    }
+}