day 5. most of the work here was getting the parsing right

05/main.rs

@@ -0,0 +1,115 @@
+#![allow(dead_code)]
+use std::collections::VecDeque;
+use std::fs::File;
+use std::io;
+use std::io::BufRead;
+use std::path::Path;
+use std::time::Instant;
+
+fn main() {
+    let now = Instant::now();
+    part_one();
+    let part_one_duration = now.elapsed();
+    part_two();
+    let part_two_duration = now.elapsed();
+    println!(
+        "p1: {}ms, p2: {}ms",
+        part_one_duration.as_millis(),
+        (part_two_duration - part_one_duration).as_millis()
+    );
+}
+
+fn read_lines<P>(filename: P) -> io::Result<io::Lines<io::BufReader<File>>>
+where
+    P: AsRef<Path>,
+{
+    // note that this discards a final newline
+    let file = File::open(filename)?;
+    Ok(io::BufReader::new(file).lines())
+}
+
+fn part_one() {
+    if let Ok(lines) = read_lines("./inputs/input") {
+        let mut stacks = vec![VecDeque::<char>::new(); 9];
+        let mut lines_parsed = 0;
+        for line in lines {
+            lines_parsed += 1;
+            // build our stacks...
+            if lines_parsed < 9 {
+                if let Ok(stack) = line {
+                    for (i, s) in stack.chars().enumerate() {
+                        if (i % 4) == 1 && s != ' ' {
+                            // we load in from the head, so the end of the vec is the "top" of the stack
+                            stacks[(i / 4)].push_front(s)
+                        }
+                    }
+                    continue;
+                }
+            }
+            if lines_parsed < 11 {
+                continue; // skip the break
+            }
+            // ok, so now we need to move the crates around
+            if let Ok(instruction) = line {
+                let steps = instruction.split(" ").collect::<Vec<&str>>();
+                let (mut count, from, to) = (
+                    steps[1].parse::<usize>().unwrap(),
+                    steps[3].parse::<usize>().unwrap(),
+                    steps[5].parse::<usize>().unwrap(),
+                );
+                while count > 0 {
+                    let c = stacks[from - 1].pop_back().unwrap();
+                    stacks[to - 1].push_back(c);
+                    count -= 1;
+                }
+            }
+        }
+        let mut result = "".to_string();
+        for mut s in stacks {
+            result.push(s.pop_back().unwrap());
+        }
+        println!("{}", result);
+    }
+}
+
+fn part_two() {
+    if let Ok(lines) = read_lines("./inputs/input") {
+        let mut stacks = vec![VecDeque::<char>::new(); 9];
+        let mut lines_parsed = 0;
+        for line in lines {
+            lines_parsed += 1;
+            // build our stacks...
+            if lines_parsed < 9 {
+                if let Ok(stack) = line {
+                    for (i, s) in stack.chars().enumerate() {
+                        if (i % 4) == 1 && s != ' ' {
+                            // we load in from the head, so the end of the vec is the "top" of the stack
+                            stacks[(i / 4)].push_front(s)
+                        }
+                    }
+                    continue;
+                }
+            }
+            if lines_parsed < 11 {
+                continue; // skip the break
+            }
+            // ok, so now we need to move the crates around
+            if let Ok(instruction) = line {
+                let steps = instruction.split(" ").collect::<Vec<&str>>();
+                let (count, from, to) = (
+                    steps[1].parse::<usize>().unwrap(),
+                    steps[3].parse::<usize>().unwrap(),
+                    steps[5].parse::<usize>().unwrap(),
+                );
+                let s = stacks[from - 1].len();
+                let mut c = stacks[from - 1].split_off(s - count);
+                stacks[to - 1].append(&mut c);
+            }
+        }
+        let mut result = "".to_string();
+        for mut s in stacks {
+            result.push(s.pop_back().unwrap());
+        }
+        println!("{}", result);
+    }
+}