Day 6 complete!

src/main.rs

@@ -8,6 +8,7 @@ mod wiremap;
 use crate::args::Command;
 use crate::endchannel::channel;
 use crate::fuel::calculate_fuel;
+use crate::orbits::Object;
 use crate::wiremap::WireMap;
 use std::cmp::{max,min};
 
@@ -105,8 +106,26 @@ fn main() {
         }
 
         Command::Orbits(uom) => {
-            println!("Got orbits.");
+            println!("Got orbits:");
+            uom.show();
             println!("Base map has {} orbits.", uom.num_orbits());
+            match uom.find_path(&Object::new("YOU"), &Object::new("SAN")) {
+                None =>
+                    println!("There is no path from you to Santa. :("),
+                Some(path) => {
+                    print!("The path from you to Santa is: ");
+                    let mut path_iter = path.iter().peekable();
+
+                    while let Some(x) = path_iter.next() {
+                        print!("{}", x);
+                        if path_iter.peek().is_some() {
+                            print!(" => ");
+                        }
+                    }
+                    println!("");
+                    println!("  ... so the number of transfers needed is {}", path.len() - 3);
+                }
+            }
         }
     }
  }

src/orbits.rs

@@ -8,6 +8,16 @@ pub enum Object {
     Object(String),
 }
 
+impl Object {
+    pub fn new(s: &str) -> Object {
+        if s == "COM" {
+            Object::CenterOfMass
+        } else {
+            Object::Object(s.to_string())
+        }
+    }
+}
+
 impl fmt::Display for Object {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
@@ -21,11 +31,7 @@ impl FromStr for Object {
     type Err = ();
 
     fn from_str(s: &str) -> Result<Object,Self::Err> {
-        if s == "COM" {
-            Ok(Object::CenterOfMass)
-        } else {
-            Ok(Object::Object(s.to_string()))
-        }
+        Ok(Object::new(s))
     }
 }
 
@@ -45,8 +51,12 @@ impl FromStr for UniversalOrbitMap {
                 continue;
             }
             let mut splits = nextline.split(')');
-            let obj1str = splits.next().unwrap_or_else(|| panic!("Bad orbit line: {}", nextline));
-            let obj2str = splits.next().unwrap_or_else(|| panic!("Bad orbit line: {}", nextline));
+            let obj1str = splits.next()
+                                .unwrap_or_else(|| panic!("Bad orbit line: {}", nextline))
+                                .trim();
+            let obj2str = splits.next()
+                                .unwrap_or_else(|| panic!("Bad orbit line: {}", nextline))
+                                .trim();
             let obj1 = Object::from_str(&obj1str)?;
             let obj2 = Object::from_str(&obj2str)?;
             if let Some(prev) = orbits.get_mut(&obj1) {
@@ -113,26 +123,104 @@ impl UniversalOrbitMap {
     }
 
     pub fn num_orbits(&self) -> usize {
-        let mut result = 0;
+        let mut search_stack = vec![(Object::CenterOfMass, 0)];
+        let mut total = 0;
 
-        for obj1 in self.objects().iter() {
-            for obj2 in self.objects().iter() {
-                if (obj1 != obj2) && self.indirectly_orbits(obj1, obj2) {
-                    result += 1;
+        while let Some((nextobj, len)) = search_stack.pop() {
+            total += len;
+
+            match self.orbits.get(&nextobj) {
+                None => { }
+                Some(objs) => {
+                    for obj in objs {
+                        search_stack.push((obj.clone(), len + 1));
+                }
             }
         }
         }
 
-        result
+        total
     }
+
+    pub fn show(&self) {
+        for (key, values) in self.orbits.iter() {
+            print!("{} => ", key);
+            for value in values.iter()  {
+                print!("{} ", value);
+            }
+            println!("");
+        }
+    }
+
+    fn path_from_origin(&self, obj: &Object) -> Option<Vec<Object>> {
+        let mut search_stack = vec![(Object::CenterOfMass, vec![Object::CenterOfMass])];
+        let mut total = 0;
+
+        while let Some((nextobj, mut path)) = search_stack.pop() {
+            if &nextobj == obj {
+                path.push(nextobj);
+                return Some(path);
+            }
+
+            match self.orbits.get(&nextobj) {
+                None => { }
+                Some(objs) => {
+                    path.push(nextobj);
+                    for obj in objs {
+                        search_stack.push((obj.clone(), path.clone()));
+                    }
+                }
+            }
+        }
+
+        panic!("Can't reach object from origin: {}", obj);
+    }
+
+    pub fn find_path(&self, obj1: &Object, obj2: &Object) -> Option<Vec<Object>> {
+        let obj1path = self.path_from_origin(obj1)?; 
+        let obj2path = self.path_from_origin(obj2)?; 
+
+        println!("path1: {:?}", obj1path);
+        println!("path2: {:?}", obj2path);
+
+        let joinpoint = find_join_point(&obj1path, &obj2path)?;
+
+        let path1stub = obj1path.iter().skip_while(|x| x != &&joinpoint);
+        let path2stub = obj2path.iter().skip_while(|x| x != &&joinpoint);
+
+        let mut result = vec![];
+
+        for x in path1stub { result.push(x.clone()); }
+        result.reverse();
+        for x in path2stub.skip(1) { result.push(x.clone()); }
+        println!("result: {:?}", result);
+
+        Some(result)
+    }
+}
+
+fn find_join_point<T: Clone + PartialEq>(list1: &Vec<T>, list2: &Vec<T>) -> Option<T> {
+    for possible in list1.iter().rev() {
+        if list2.contains(possible) {
+            return Some(possible.clone());
+        }
+    }
+    None
 }
 
 #[test]
 fn examples() {
-    let input = "COM)B\nB)C\nC)D\nD)E\nE)F\nB)G\nG)H\nD)I\nE)J\nJ)K\nK)L";
-    let map = UniversalOrbitMap::from_str(&input).unwrap();
-    assert!(map.orbits(&Object::Object("B".to_string()), &Object::CenterOfMass));
-    assert!(map.indirectly_orbits(&Object::Object("B".to_string()), &Object::CenterOfMass));
-    assert!(map.indirectly_orbits(&Object::Object("E".to_string()),&Object::CenterOfMass));
+    let input1 = "COM)B\nB)C\nC)D\nD)E\nE)F\nB)G\nG)H\nD)I\nE)J\nJ)K\nK)L";
+    let map = UniversalOrbitMap::from_str(&input1).unwrap();
+    assert!(map.orbits(&Object::new("B"), &Object::CenterOfMass));
+    assert!(map.indirectly_orbits(&Object::new("B"), &Object::CenterOfMass));
+    assert!(map.indirectly_orbits(&Object::new("E"),&Object::CenterOfMass));
     assert_eq!(map.num_orbits(), 42);
+    let day6_contents = std::fs::read("inputs/day6").unwrap();
+    let day6_str = std::str::from_utf8(&day6_contents).unwrap();
+    let day6map = UniversalOrbitMap::from_str(&day6_str).unwrap();
+    assert_eq!(day6map.num_orbits(), 204521);
+    let input2 = "COM)B\nB)C\nC)D\nD)E\nE)F\nB)G\nG)H\nD)I\nE)J\nJ)K\nK)L\nK)YOU\nI)SAN";
+    let map2 = UniversalOrbitMap::from_str(input2).unwrap();
+    assert_eq!(map2.find_path(&Object::new("YOU"), &Object::new("SAN")).unwrap().len(), 7);
 }