two-bucket: test inability to reach the goal

exercises/two-bucket/example.rs

@@ -31,7 +31,7 @@ pub struct BucketStats {
 }
 
 /// Solve the bucket problem
-pub fn solve(capacity_1: u8, capacity_2: u8, goal: u8, start_bucket: &Bucket) -> BucketStats {
+pub fn solve(capacity_1: u8, capacity_2: u8, goal: u8, start_bucket: &Bucket) -> Option<BucketStats> {
     let state = match *start_bucket {
         Bucket::One => (capacity_1, 0),
         Bucket::Two => (0, capacity_2),
@@ -48,25 +48,25 @@ pub fn solve(capacity_1: u8, capacity_2: u8, goal: u8, start_bucket: &Bucket) ->
     visited.insert((capacity_1, 0));
     visited.insert((0, capacity_2));
 
-    loop {
+    while !next_search.is_empty() {
         let mut current_search = next_search;
         next_search = VecDeque::new();
 
         for state in current_search.drain(0..) {
             let (bucket_1, bucket_2) = state;
 
             if bucket_1 == goal {
-                return BucketStats {
+                return Some(BucketStats {
                     moves,
                     goal_bucket: Bucket::One,
                     other_bucket: bucket_2,
-                };
+                });
             } else if bucket_2 == goal {
-                return BucketStats {
+                return Some(BucketStats {
                     moves,
                     goal_bucket: Bucket::Two,
                     other_bucket: bucket_1,
-                };
+                });
             }
 
             // Empty the first bucket
@@ -122,4 +122,7 @@ pub fn solve(capacity_1: u8, capacity_2: u8, goal: u8, start_bucket: &Bucket) ->
 
         moves += 1;
     }
+
+    // We ran out of states to search but still didn't reach the goal.
+    None
 }

exercises/two-bucket/src/lib.rs

@@ -17,9 +17,9 @@ pub struct BucketStats {
 }
 
 /// Solve the bucket problem
-pub fn solve(capacity_1: u8, capacity_2: u8, goal: u8, start_bucket: &Bucket) -> BucketStats {
+pub fn solve(capacity_1: u8, capacity_2: u8, goal: u8, start_bucket: &Bucket) -> Option<BucketStats> {
     unimplemented!(
-        "Given one bucket of capacity {}, another of capacity {}, starting with {:?}, find pours to reach {}",
+        "Given one bucket of capacity {}, another of capacity {}, starting with {:?}, find pours to reach {}, or None if impossible",
         capacity_1,
         capacity_2,
         start_bucket,

exercises/two-bucket/tests/two-bucket.rs

@@ -4,11 +4,11 @@ use two_bucket::{solve, Bucket, BucketStats};
 fn test_case_1() {
     assert_eq!(
         solve(3, 5, 1, &Bucket::One),
-        BucketStats {
+        Some(BucketStats {
             moves: 4,
             goal_bucket: Bucket::One,
             other_bucket: 5,
-        }
+        })
     );
 }
 
@@ -17,11 +17,11 @@ fn test_case_1() {
 fn test_case_2() {
     assert_eq!(
         solve(3, 5, 1, &Bucket::Two),
-        BucketStats {
+        Some(BucketStats {
             moves: 8,
             goal_bucket: Bucket::Two,
             other_bucket: 3,
-        }
+        })
     );
 }
 
@@ -30,11 +30,11 @@ fn test_case_2() {
 fn test_case_3() {
     assert_eq!(
         solve(7, 11, 2, &Bucket::One),
-        BucketStats {
+        Some(BucketStats {
             moves: 14,
             goal_bucket: Bucket::One,
             other_bucket: 11,
-        }
+        })
     );
 }
 
@@ -43,11 +43,11 @@ fn test_case_3() {
 fn test_case_4() {
     assert_eq!(
         solve(7, 11, 2, &Bucket::Two),
-        BucketStats {
+        Some(BucketStats {
             moves: 18,
             goal_bucket: Bucket::Two,
             other_bucket: 7,
-        }
+        })
     );
 }
 
@@ -56,11 +56,11 @@ fn test_case_4() {
 fn goal_equal_to_start_bucket() {
     assert_eq!(
         solve(1, 3, 3, &Bucket::Two),
-        BucketStats {
+        Some(BucketStats {
             moves: 1,
             goal_bucket: Bucket::Two,
             other_bucket: 0,
-        }
+        })
     );
 }
 
@@ -69,10 +69,32 @@ fn goal_equal_to_start_bucket() {
 fn goal_equal_to_other_bucket() {
     assert_eq!(
         solve(2, 3, 3, &Bucket::One),
-        BucketStats {
+        Some(BucketStats {
             moves: 2,
             goal_bucket: Bucket::Two,
             other_bucket: 2,
-        }
+        })
+    );
+}
+
+#[test]
+#[ignore]
+fn not_possible_to_reach_the_goal() {
+    assert_eq!(
+        solve(6, 15, 5, &Bucket::One),
+        None
+    );
+}
+
+#[test]
+#[ignore]
+fn with_same_buckets_but_different_goal_then_it_is_possible() {
+    assert_eq!(
+        solve(6, 15, 9, &Bucket::One),
+        Some(BucketStats {
+            moves: 10,
+            goal_bucket: Bucket::Two,
+            other_bucket: 0,
+        })
     );
 }