operating on numeric ids instead of strings

day8/src/main.rs

@@ -1,14 +1,13 @@
 use std::fs::read_to_string;
-use std::collections::HashMap;
 use num::integer::lcm;
 
-fn get_steps_to(directions: &str, nodes: &HashMap<&str, (&str, &str)>,
-                start: &str, stop: fn(&str) -> bool) -> u64 {
+fn get_steps_to<F: Fn(u16) -> bool>(directions: &str, nodes: &Vec<(u16, u16)>,
+                                    start: u16, stop: F) -> u64 {
     let mut current_node = start;
     let mut counter: u64 = 0;
     'outer: loop {
         for c in directions.bytes() {
-            let (left, right) = nodes[current_node];
+            let (left, right) = nodes[current_node as usize];
             match c {
                 b'L' => current_node = left,
                 b'R' => current_node = right,
@@ -23,22 +22,36 @@ fn get_steps_to(directions: &str, nodes: &HashMap<&str, (&str, &str)>,
     counter
 }
 
+fn str_to_id(str: &str) -> u16 {
+    let mut value: u16 = 0;
+    for c in str.bytes() {
+        value = value * 26 + (c - b'A') as u16;
+    }
+    value
+}
+
 fn main() {
     let lines_str = read_to_string("input.txt").unwrap();
     let mut lines_iter = lines_str.lines();
     let directions = lines_iter.next().unwrap();
     lines_iter.next();
-    let nodes = lines_iter.map(|line| {
+    let mut nodes: Vec<(u16, u16)> = vec![(0, 0); 17576];
+    let mut ids_ending_with_a: Vec<u16> = Vec::new();
+    for line in lines_iter {
         let mut ids = line.split([' ', '(', ')', '=', ',']).filter(|&str| !str.is_empty());
-        (ids.next().unwrap(), (ids.next().unwrap(), ids.next().unwrap()))
-    }).collect::<HashMap<_, _>>();
-    let counter1 = get_steps_to(directions, &nodes, "AAA", |str| str == "ZZZ");
-    let counter2 = nodes.iter()
-        .filter_map(|(&id, _)|
-            Some(id).filter(|&id| id.as_bytes()[2 as usize] == b'A'))
-        .map(|node| get_steps_to(
-            directions, &nodes, node, |str| str.as_bytes()[2 as usize] == b'Z'))
+        let node_id = str_to_id(ids.next().unwrap());
+        nodes[node_id as usize] = (str_to_id(ids.next().unwrap()), str_to_id(ids.next().unwrap()));
+        if node_id % 26 == 0 {
+            ids_ending_with_a.push(node_id);
+        }
+    }
+    let id_aaa = str_to_id("AAA");
+    let id_zzz = str_to_id("ZZZ");
+    let counter1 = get_steps_to(directions, &nodes, id_aaa, |id| id == id_zzz);
+    let counter2 = ids_ending_with_a.iter()
+        .map(|&node| get_steps_to(
+            directions, &nodes, node, |id| id % 26 == 25))
         .fold(1 as u64, |acc, counter| lcm(acc, counter));
-    println!("{}", counter1);
-    println!("{}", counter2);
+    println!("Counter1: {}", counter1);
+    println!("Counter2: {}", counter2);
 }