d12p1

day12/src/main.rs

@@ -2,30 +2,82 @@ use std::env;
 use std::fs::File;
 use std::io::{self, BufRead};
 use std::collections::BinaryHeap;
-use std::cmp::Reverse;
+use std::cmp::max;
 
-fn find<T: Eq + Copy>(haystack: &Vec<Vec<T>>, needle: T) -> (usize, usize) {
-    // I just wanna play around with iters; there are better ways...
-    haystack.iter().enumerate()
-        .map(|(i, &ref row)|
-            (i, row.iter().enumerate()
-                .filter(|(_j, &ref c)| *c == needle)
-                .map(|(j, _c)| j)
-                .collect::<Vec<usize>>()))
-        .filter(|(_i, row)| !row.is_empty())
-        .map(|(i, row)| (i, *row.iter().nth(0).unwrap()))
-        .nth(0).unwrap()
+fn get(map: &Vec<Vec<i64>>, coord: (usize, usize)) -> i64 {
+    map[coord.0 as usize][coord.1 as usize]
 }
 
 fn main() {
     let file = File::open(&env::args().nth(1).unwrap()).unwrap();
-    let map: Vec<Vec<u8>> = io::BufReader::new(file).lines().flatten()
-        .map(|line| line.chars().map(|c| c as u8).collect())
-        .collect();
-    let (starti, startj) = find(&map, 'S' as u8);
-    let (endi, endj) = find(&map, 'E' as u8);
+    let mut map: Vec<Vec<i64>> = Vec::new();
+    let mut queue = BinaryHeap::new();
+    let (mut start, mut end) = ((0, 0), (0, 0));
 
-    println!("{:?}", map);
-    println!("{:?}, {:?} -> {:?}, {:?}", starti, startj, endi, endj);
+    // parse input
+    for (i, line) in io::BufReader::new(file).lines().flatten().enumerate() {
+        let mut row: Vec<i64> = Vec::new();
+        for (j, c) in line.chars().enumerate() {
+            match c {
+                'S' => { start = (i, j); row.push('a' as i64); },
+                'E' => { end = (i, j); row.push('z' as i64); },
+                c => row.push(c as i64),
+            }
+        }
+        map.push(row);
+    }
+    let (height, width) = (map.len(), map[0].len());
+    let mut costs = vec![vec![i64::MAX; width]; height];
+    let heur: Vec<Vec<i64>> = (0..height)
+        .map(|i| (0..width)
+            .map(|j|
+                max((i.abs_diff(end.0) + j.abs_diff(end.1)) as i64,
+                    get(&map, end) - get(&map, (i, j))))
+            .collect())
+        .collect();
+        
+    queue.push((-heur[start.0][start.1], start));
+    costs[start.0][start.1] = 0;
+
+    // A*
+    let answer = loop {
+        // no route
+        if queue.is_empty() {
+            break None;
+        }
+
+        let (_, (i, j)) = queue.pop().unwrap();
+        let cost = get(&costs, (i, j));
+
+        // found destination
+        if (i, j) == end {
+            break Some(cost);
+        }
+
+        // handle neighbors
+        let neighbors = [
+            (i as i64, (j as i64) - 1),
+            (i as i64, (j as i64) + 1),
+            ((i as i64) - 1, j as i64),
+            ((i as i64) + 1, j as i64)];
+        for (nexti, nextj) in neighbors {
+            if nexti < 0 || nextj < 0
+                || nexti >= height as i64 || nextj >= width as i64
+                || map[nexti as usize][nextj as usize] > map[i][j] + 1
+            {
+                continue;
+            }
+            let nexti: usize = nexti as usize;
+            let nextj: usize = nextj as usize;
+            let new_cost = cost + 1;
+            if new_cost < costs[nexti][nextj] {
+                costs[nexti][nextj] = new_cost;
+                queue.retain(|(_, (ri, rj))| *ri != nexti || *rj != nextj);
+                queue.push((-new_cost - heur[nexti][nextj], (nexti, nextj)));
+            }
+        }
+    };
+
+    println!("= {:?}", answer);
 }