From 010cf84aa0d3641f9f5140343b1ca194b6aa3caf Mon Sep 17 00:00:00 2001
From: William Brawner <me@wbrawner.com>
Date: Mon, 5 Dec 2022 13:49:23 -0700
Subject: [PATCH] Add solution for day 5

---
 rust/src/bin/day05.rs | 104 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 rust/src/bin/day05.rs

diff --git a/rust/src/bin/day05.rs b/rust/src/bin/day05.rs
new file mode 100644
index 0000000..75bc358
--- /dev/null
+++ b/rust/src/bin/day05.rs
@@ -0,0 +1,104 @@
+use rust::util::read_input;
+use std::collections::VecDeque;
+
+fn build_stacks(input: &Vec<String>) -> Vec<VecDeque<char>> {
+    let mut stacks: Vec<VecDeque<char>> = vec![];
+    input
+        .iter()
+        .take_while(|line| !line.trim_start().starts_with("1"))
+        .for_each(|line| {
+            line.char_indices().for_each(|(i, c)| {
+                if i == 0 || (i - 1) % 4 != 0 {
+                    return;
+                }
+                let stack_index = (i - 1) / 4;
+                if stack_index >= stacks.len() {
+                    let mut stack = VecDeque::new();
+                    if c != ' ' {
+                        stack.push_front(c);
+                    }
+                    stacks.push(stack);
+                } else {
+                    if c != ' ' {
+                        stacks[stack_index].push_front(c);
+                    }
+                }
+            })
+        });
+    stacks
+}
+
+fn part1(input: &Vec<String>) -> String {
+    let mut stacks = build_stacks(&input);
+    input
+        .iter()
+        .skip_while(|line| !line.starts_with("move"))
+        .for_each(
+            |line| match line.split(' ').collect::<Vec<&str>>().as_slice() {
+                [_, amount_str, _, from_index_str, _, to_index_str] => {
+                    let from_index = usize::from_str_radix(from_index_str, 10)
+                        .expect("failed to parse from_index")
+                        - 1;
+                    let to_index = usize::from_str_radix(to_index_str, 10)
+                        .expect("failed to parse to_index")
+                        - 1;
+                    let amount =
+                        usize::from_str_radix(amount_str, 10).expect("failed to parse amount");
+                    for _ in 0..amount {
+                        let from = stacks[from_index]
+                            .pop_back()
+                            .expect("invalid instruction: attempted to move from empty stack");
+                        let to = &mut stacks[to_index];
+                        to.push_back(from);
+                    }
+                }
+                _ => panic!("invalid instruction"),
+            },
+        );
+    stacks
+        .iter()
+        .map(|stack| stack.back().unwrap_or(&' '))
+        .collect::<String>()
+}
+
+fn part2(input: &Vec<String>) -> String {
+    let mut stacks = build_stacks(&input);
+    input
+        .iter()
+        .skip_while(|line| !line.starts_with("move"))
+        .for_each(
+            |line| match line.split(' ').collect::<Vec<&str>>().as_slice() {
+                [_, amount_str, _, from_index_str, _, to_index_str] => {
+                    let from_index = usize::from_str_radix(from_index_str, 10)
+                        .expect("failed to parse from_index")
+                        - 1;
+                    let to_index = usize::from_str_radix(to_index_str, 10)
+                        .expect("failed to parse to_index")
+                        - 1;
+                    let amount =
+                        usize::from_str_radix(amount_str, 10).expect("failed to parse amount");
+                    let amount_index = stacks[from_index].len() - amount;
+                    let from = stacks[from_index].split_off(amount_index);
+                    let to = &mut stacks[to_index];
+                    for item in from {
+                        to.push_back(item);
+                    }
+                }
+                _ => panic!("invalid instruction"),
+            },
+        );
+    stacks
+        .iter()
+        .map(|stack| stack.back().unwrap_or(&' '))
+        .collect::<String>()
+}
+
+fn main() {
+    let test_input = read_input("Day05_test").expect("Failed to open test input");
+    assert_eq!("CMZ", part1(&test_input));
+    assert_eq!("MCD", part2(&test_input));
+
+    let input = read_input("Day05").expect("Failed to open input");
+    println!("{:?}", part1(&input));
+    println!("{:?}", part2(&input));
+}