day05: Changes for part 2

I feel like there should be away for me to read from the back and move
things over directly instead of having a temporary Vec for it, but I'm
not sure how this would work with the owner-checking, so I didn't try.

day05/Cargo.lock

@@ -0,0 +1,42 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "aho-corasick"
+version = "0.7.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc936419f96fa211c1b9166887b38e5e40b19958e5b895be7c1f93adec7071ac"
+dependencies = [
+ "memchr",
+]
+
+[[package]]
+name = "day05"
+version = "0.1.0"
+dependencies = [
+ "regex",
+]
+
+[[package]]
+name = "memchr"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
+
+[[package]]
+name = "regex"
+version = "1.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e076559ef8e241f2ae3479e36f97bd5741c0330689e217ad51ce2c76808b868a"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.6.28"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "456c603be3e8d448b072f410900c09faf164fbce2d480456f50eea6e25f9c848"

day05/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "day05"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+regex = "1.7.0"

day05/src/main.rs

@@ -0,0 +1,69 @@
+use std::error;
+use std::fs::File;
+use std::io::BufRead;
+use std::io::BufReader;
+
+use regex::Regex;
+
+fn main() -> Result<(), Box<dyn error::Error>> {
+	let f = File::open("input.txt")?;
+	let reader = BufReader::new(f);
+
+	let mut lines = reader.lines();
+
+	let mut items: Vec<Vec<&str>> = Vec::new();
+
+	// read the initial state
+	let mut init_lines: Vec<String> = vec![];
+	while let Some(Ok(line)) = lines.next() {
+		if line == "" {
+			break;
+		}
+		init_lines.push(line);
+	}
+
+	init_lines.reverse();
+	let mut count = 0;
+	for (i, line) in init_lines.iter().enumerate() {
+		// init the items with the right amount of Vecs
+		if i == 0 {
+			count = line.split_whitespace().count();
+			for _ in 0..count {
+				items.push(vec![]);
+			}
+			continue;
+		}
+
+		// add the items to the vecs
+		// let line_iter = line.chars();
+		for i in 0..count {
+			let item = &line[(i * 4 + 1)..(i * 4 + 2)];
+			if item == " " {
+				continue;
+			}
+			items[i].push(&item);
+		}
+	}
+
+	// read the movements
+	let re = Regex::new(r"^move (\d+) from (\d+) to (\d+)$")?;
+	while let Some(Ok(line)) = lines.next() {
+		// println!("{:?}", re.captures(&line));
+		// println!("{:?}", items);
+		let cap: Vec<usize> = re.captures(&line).ok_or("Could not match line")?.iter().skip(1).map(|x| x.unwrap().as_str().parse().unwrap()).collect();
+		let mut items_to_move = vec![];
+		for _ in 0..cap[0] {
+			let item = items[cap[1] - 1].pop().ok_or("Found a broken match")?;
+			items_to_move.push(item);
+		}
+
+		for item in items_to_move.iter().rev() {
+			items[cap[2] - 1].push(item);
+		}
+	}
+
+    // output the result (top of each item-stack i.e. end of the Vec)
+	// println!("{:?}", items);
+    println!("{}", items.iter().map(|v| String::from(*v.iter().last().unwrap())).collect::<Vec<_>>().join(""));
+    Ok(())
+}