day01 and day03 part 2 solutions

2016/day01/src/main.rs

@@ -20,6 +20,10 @@ fn step(state: &(i32, i32), pos: &(i32, i32), dist: i32) -> (i32, i32) {
     (pos.0 + state.0 * dist, pos.1 + state.1 * dist)
 }
 
+fn tiny_step(state: &(i32, i32), pos: &(usize, usize)) -> (usize, usize) {
+    ((pos.0 as i32 + state.0) as usize, (pos.1 as i32 + state.1) as usize)
+}
+
 fn part_1(input: &String) {
     let mut state = (1, 0);
     let mut pos = (0, 0);
@@ -37,26 +41,29 @@ fn part_1(input: &String) {
 }
 
 fn part_2(input: &String) {
-    let mut state = (1, 0);
-    let mut positions: Vec<(i32, i32)> = vec![(0, 0)];
+    const OFFSET: usize = 500; //we'll make a grid 1000x1000
+    let mut grid = [[false; 2*OFFSET]; 2*OFFSET];
 
-    for item in input.trim().split(", ") {
+    let mut state = (1, 0);
+    let mut pos = (OFFSET, OFFSET);
+    grid[OFFSET][OFFSET] = true; //we are already at the axis
+
+    'outer: for item in input.trim().split(", ") {
         let (dir, dist) = item.split_at(1);
         let dir: String = dir.to_string();
-        let dist: i32 = dist.parse::<i32>().unwrap();
+        let mut dist: i32 = dist.parse::<i32>().unwrap();
 
         state = turn(&state, &dir);
-        let pos = step(&state, positions.last().unwrap(), dist);
-        print!("{}: {}{} -> ({}, {}), ", positions.len(), dist, dir, pos.0, pos.1);
-        match positions.iter().position(|&p| p == pos) {
-            Some(v) => {
-                println!("Part 2: Stopped twice at ({}, {}) on element {}, {} away from the start", pos.0, pos.1, v, pos.0.abs() + pos.1.abs());
-                break;
-            },
-            None => {
-                //println!("Did not match {} locations", positions.len());
-                positions.push(pos);
-            },
+        while dist > 0 { //take a step
+            pos = tiny_step(&state, &pos);
+            match grid[pos.0][pos.1] {
+                true => {
+                    let real_pos = ((pos.0 as i32 - OFFSET as i32), (pos.1 as i32 - OFFSET as i32));
+                    println!("Part 2: Returned to ({}, {}), {} away from the start", real_pos.0, real_pos.1, real_pos.0.abs() + real_pos.1.abs());
+                    break 'outer;
+                },
+                false => { grid[pos.0][pos.1] = true; dist = dist - 1 },
+            }
         }
     }
 }
@@ -66,6 +73,6 @@ fn main() {
     let mut input = String::new();
     file.read_to_string(&mut input).expect("could not read file");
 
-    //part_1(&input);
+    part_1(&input);
     part_2(&input);
 }