From cd108514a2eb4ed2e799a01b186c214799d0dfbb Mon Sep 17 00:00:00 2001
From: cmccandless <cmccandless@users.noreply.github.com>
Date: Thu, 12 Oct 2017 13:45:36 -0500
Subject: [PATCH] two-bucket: Fix incorrect test case to resolve #794

---
 exercises/two-bucket/example.py         | 103 +++++++++++-------------
 exercises/two-bucket/two_bucket_test.py |   2 +-
 2 files changed, 50 insertions(+), 55 deletions(-)

diff --git a/exercises/two-bucket/example.py b/exercises/two-bucket/example.py
index 3bca958aca..f27380e113 100644
--- a/exercises/two-bucket/example.py
+++ b/exercises/two-bucket/example.py
@@ -1,59 +1,54 @@
 '''
-The solution follows the following approach:
-
-->Pour from first bucket to second
-  1.Fill the first bucket and empty it into the second bucket.
-  2.If first bucket is empty fill it.
-  3.If the second bucket is full empty it.
-  4.Repeat steps 1,2,3 till either the first or second bucket contains the
-    desired amount.
-
-->Pour from first bucket to second
-  1.Fill the second bucket and empty it into the first bucket.
-  2.If second bucket is empty fill it.
-  3.If the firts bucket is full empty it.
-  4.Repeat steps 1,2,3 till either the first or second bucket contains the
-    desired amount.
+    This solution implements a breadth-first search of the graph
+    of possible valid states for the two buckets until it reaches a state
+    in which one of the two buckets contains the goal amount
 '''
 
 
 def two_bucket(bucket_one_cap, bucket_two_cap, desired_liters, first):
-    if first == "one":
-        moves = 0
-        bucket_one, bucket_two = 0, 0
-        while(True):
-            if bucket_one == 0:
-                moves += 1
-                bucket_one = bucket_one_cap
-            elif bucket_two == bucket_two_cap:
-                moves += 1
-                bucket_two = 0
-            else:
-                moves += 1
-                measure = min(bucket_one, bucket_two_cap - bucket_two)
-                bucket_one -= measure
-                bucket_two += measure
-            if bucket_one == desired_liters:
-                return (moves, "one", bucket_two)
-            elif bucket_two == desired_liters:
-                return (moves, "two", bucket_one)
-
-    elif first == "two":
-        moves = 0
-        bucket_one, bucket_two = 0, 0
-        while(True):
-            if bucket_two == 0:
-                moves += 1
-                bucket_two = bucket_two_cap
-            elif bucket_one == bucket_one_cap:
-                moves += 1
-                bucket_one = 0
-            else:
-                moves += 1
-                measure = min(bucket_two, bucket_one_cap - bucket_one)
-                bucket_two -= measure
-                bucket_one += measure
-            if bucket_one == desired_liters:
-                return (moves, "one", bucket_two)
-            elif bucket_two == desired_liters:
-                return (moves, "two", bucket_one)
+    sizes = [bucket_one_cap, bucket_two_cap]
+    goal = desired_liters
+    goalIndex = 0 if first == 'one' else 1
+
+    def empty(buckets, i):
+        return [0, buckets[1]] if i == 0 else [buckets[0], 0]
+
+    def fill(buckets, i):
+        return [sizes[0], buckets[1]] if i == 0 else [buckets[0], sizes[1]]
+
+    def consolidate(buckets, i):
+        amount = min(buckets[1 - i], sizes[i] - buckets[i])
+        target = buckets[i] + amount
+        src = buckets[1 - i] - amount
+        return [target, src] if i == 0 else [src, target]
+
+    def bucket_str(buckets):
+        return '{},{}'.format(*buckets)
+
+    invalid = [0, 0]
+    invalid[1 - goalIndex] = sizes[1 - goalIndex]
+    invalidStr = bucket_str(invalid)
+    buckets = [0, 0]
+    buckets[goalIndex] = sizes[goalIndex]
+    toVisit = []
+    visited = set()
+    count = 1
+    while goal not in buckets:
+        key = bucket_str(buckets)
+        if key != invalidStr and key not in visited:
+            visited.add(key)
+            nc = count + 1
+            for i in range(2):
+                if buckets[i] != 0:
+                    toVisit.append((empty(buckets, i), nc))
+                if buckets[i] != sizes[i]:
+                    toVisit.append((fill(buckets, i), nc))
+                    toVisit.append((consolidate(buckets, i), nc))
+        if not any(toVisit):
+            raise ValueError('No more moves!')
+        buckets, count = toVisit.pop(0)
+
+    goalIndex = buckets.index(goal)
+    goalBucket = ['one', 'two'][goalIndex]
+    otherBucket = buckets[1 - goalIndex]
+    return (count, goalBucket, otherBucket)
diff --git a/exercises/two-bucket/two_bucket_test.py b/exercises/two-bucket/two_bucket_test.py
index 0b07d50105..5787ef82c7 100644
--- a/exercises/two-bucket/two_bucket_test.py
+++ b/exercises/two-bucket/two_bucket_test.py
@@ -25,7 +25,7 @@ def test_bucket_one_size_1_bucket_two_size_3_start_with_bucket_two(self):
         self.assertEqual(two_bucket(1, 3, 3, "two"), (1, "two", 0))
 
     def test_bucket_one_size_2_bucket_two_size_3_start_with_bucket_one(self):
-        self.assertEqual(two_bucket(2, 3, 3, "one"), (4, "two", 1))
+        self.assertEqual(two_bucket(2, 3, 3, "one"), (2, "two", 2))
 
 
 if __name__ == '__main__':