After bruteforcing, implemented reverse map.

src/days/day5.rs

@@ -19,6 +19,16 @@ impl RangeMap {
             None
         }
     }
+
+    fn inverse_map(&self, input: u32) -> Option<u32> {
+        let upper_bound: u64 = self.dest as u64 + self.length as u64;
+        if input >= self.dest && (input as u64) < upper_bound {
+            Some(input - self.dest + self.start)
+        }
+        else {
+            None
+        }
+    }
 }
 
 #[derive(Debug)]
@@ -36,6 +46,16 @@ impl Mapping {
         }
         input
     }
+
+    fn inverse_map(self: &Self, input: u32) -> u32 {
+        for range_map in self.range_maps.iter() {
+            match range_map.inverse_map(input) {
+                Some(x) => return x,
+                None => continue
+            }
+        }
+        input 
+    }
 }
 
 #[derive(Debug)]
@@ -64,23 +84,41 @@ impl Almanac {
         }
     }
 
-    fn find_closest(self: &Self) -> u32 {
-        let total_mapping = vec![
+    fn find_closest(self: &Self, forward: bool) -> Result<u32, AdventError> {
+        let mut total_mapping = vec![
             &self.seed_to_soil_map,
             &self.soil_to_fertilizer_map,
             &self.fertilizer_to_water_map,
             &self.water_to_light_map,
             &self.light_to_temperature_map,
             &self.temperature_to_humidity_map,
-            &self.humidity_to_location_map
+            &self.humidity_to_location_map,
         ];
-        self.seeds.clone().into_iter().map(|seed| {
-            total_mapping
-            .iter()
-            .fold(seed, | input, map| {
-                map.map(input)
-            })
-        }).min().unwrap()
+        
+        if forward {
+            self.seeds.iter().map(|seed| {
+                total_mapping
+                .iter()
+                .fold(*seed, | input, map| {
+                    map.map(input)
+                })
+            }).min().ok_or(AdventError("mapping procedure went wrong".into()))
+        } else {
+            total_mapping.reverse();
+            for loc in 0..u32::MAX {
+                let seed = total_mapping
+                .iter()
+                .fold(loc, | input, map| {
+                    map.inverse_map(input)
+                });
+                match self.seeds.binary_search(&seed) {
+                    Ok(_) => return Ok(loc),
+                    Err(_) => continue
+                }
+            };
+            Err(AdventError("Scanned location space, found nothing".into()))
+        }
+       
     }
 
     fn interpret_range(self: &mut Self) -> () {
@@ -91,7 +129,8 @@ impl Almanac {
                 vec.push(seed);
             }
         }
-        self.seeds = vec;
+        vec.sort();
+        self.seeds = vec
     }
 }
 
@@ -178,12 +217,12 @@ impl FromStr for Almanac {
 pub fn one() -> Result<u32, AdventError>
 {
     let almanac = read_into::<Almanac>(Path::new("resources/input5.txt".into()))?;
-    Ok(almanac.find_closest())
+    Ok(almanac.find_closest(true)?)
 }
 
 pub fn two() -> Result<u32, AdventError>
 {
     let mut almanac = read_into::<Almanac>(Path::new("resources/input5.txt".into()))?;
     almanac.interpret_range();
-    Ok(almanac.find_closest())
+    Ok(almanac.find_closest(false)?)
 }