day 5

better understood how to use the map function

day_5/src/main.rs

@@ -1,3 +1,76 @@
-fn main() {
-    println!("Hello, world!");
+use std::{array::from_fn, fs::read_to_string, ops::Deref};
+
+const STACK_COUNT: usize = 9;
+const STACK_WIDTH: usize = 4;
+
+const PATH: &str = "src/input";
+
+fn top_of_stack(stacks: [String; STACK_COUNT]) -> String {
+    return stacks
+        .map(|s| s.chars().last().unwrap_or('?').clone().to_string())
+        .join("");
+}
+
+fn main() {
+    let binding = read_to_string(PATH).expect("Error reading file");
+    let mut data = binding.split("\n").into_iter().peekable();
+
+    // NOTE: ALSO COPIES NUMBERS AT BOTTOM OF STACKS. SHOULD HAVE NO EFFECT.
+    // READ STACKS
+    let mut stacks: [String; STACK_COUNT] = from_fn(|_x| String::new());
+    while data.peek().is_some() && data.peek().expect("expected string").deref().len() > 0 {
+        let row = data.next().unwrap_or("");
+        for i in 0..STACK_COUNT {
+            let item = row
+                .get(STACK_WIDTH * i + 1..STACK_WIDTH * i + 2)
+                .unwrap_or("");
+            if item.chars().all(char::is_alphanumeric) {
+                stacks[i].push_str(item);
+            }
+        }
+    }
+
+    // inefficient
+    for i in 0..STACK_COUNT {
+        stacks[i] = stacks[i].chars().rev().collect::<String>();
+    }
+    let mut stacks_pt_2 = stacks.clone();
+
+    // SKIP EMPTY LINE
+    data.next();
+
+    // PROCESS INSTRUCTIONS
+    while data.peek().is_some() && data.peek().expect("expected string").deref().len() > 0 {
+        let mut tokens = data.next().unwrap_or("").split_ascii_whitespace();
+
+        macro_rules! get_token {
+            () => {
+                tokens.nth(1).unwrap().parse::<usize>().unwrap()
+            };
+        }
+
+        let n_move = get_token!();
+        let src = get_token!() - 1;
+        let dest = get_token!() - 1;
+        // println!("move {} from {}->{}", n_move, src, dest);
+
+        let mut pt2_buf = String::new();
+
+        for _i in 0..n_move {
+            let c = stacks[src].pop().unwrap_or('\0');
+            stacks[dest].push(c as char);
+
+            // I know it is possible to append a whole string at once but this is a quicker solution to write.
+            let c = stacks_pt_2[src].pop().unwrap_or('\0');
+            pt2_buf.push(c as char);
+        }
+        stacks_pt_2[dest].push_str(&pt2_buf.chars().rev().collect::<String>());
+        print!("");
+    }
+
+    println!(
+        "PART 1 {}\nPART 2 {}",
+        top_of_stack(stacks),
+        top_of_stack(stacks_pt_2)
+    );
 }