add day 12, part 2

day12/common.rs

@@ -89,7 +89,7 @@ impl Map {
         self.end_pos
     }
 
-    fn neighbors(&self, pos: (usize, usize)) -> Option<Vec<(usize, usize)>> {
+    pub fn neighbors(&self, pos: (usize, usize)) -> Option<Vec<(usize, usize)>> {
         let mut result = vec![];
         let height = self.square_height(pos)?;
         let (x, y) = pos;
@@ -133,10 +133,13 @@ impl Map {
         result
     }
 
-    pub fn shortest_path(&self) -> ShortestPath {
+    pub fn shortest_path(&self, start_pos: Option<(usize, usize)>) -> ShortestPath {
         // we reverse start_pos and end_pos so the ShortestPath will have the right order
+        let end_pos = match start_pos {
+            Some(pos) => pos,
+            None => self.start_pos,
+        };
         let start_pos = self.end_pos;
-        let end_pos = self.start_pos;
 
         let mut table = self.dijkstra_table(start_pos);
         let mut unvisited: HashSet<(usize, usize)> = table.iter().map(|i| i.pos).collect();
@@ -163,6 +166,18 @@ impl Map {
             start_pos: start_pos,
         }
     }
+
+    pub fn lowest_positions(&self) -> Vec<(usize, usize)> {
+        let mut result = vec![];
+        for y in 0..self.squares.len() {
+            for x in 0..self.squares[0].len() {
+                if self.squares[y][x] as char == 'a' {
+                    result.push((x, y));
+                }
+            }
+        }
+        result
+    }
 }
 
 impl Iterator for ShortestPath {
@@ -178,7 +193,7 @@ impl Iterator for ShortestPath {
             .iter()
             .find(|i| i.pos == self.current)
             .unwrap();
-        self.current = info.previous.unwrap();
+        self.current = info.previous?;
         Some(result)
     }
 }

day12/part1.rs

@@ -21,6 +21,6 @@ use common::Map;
 
 fn main() -> Result<(), &'static str> {
     let map = Map::from_stdin()?;
-    println!("{:?}", map.shortest_path().count());
+    println!("{:?}", map.shortest_path(None).count());
     Ok(())
 }