* Improve 2opt algorithm (don't enforce i to be lower than j)

1 files changed, 9 insertions, 4 deletions

diff --git a/tsp.py b/tsp.py
index b6f702c..55278a8 100755
--- a/tsp.py
+++ b/tsp.py
@@ -219,10 +219,15 @@ class Algo_2opt (Algo):
                 best = path
 
     def do_2opt (self, path):
-        i, j = sorted (random.sample (path, 2))
-        segment = path[i + 1:j]
-        segment.reverse ()
-        return Path (self.context, path[0:i + 1] + segment + path[j:])
+        i, j = random.sample (path, 2)
+        if i < j:
+            segment = path[i + 1:j]
+            segment.reverse ()
+            return Path (self.context, path[:i + 1] + segment + path[j:])
+        else:
+            segment = path[i + 1:] + path[:j]
+            segment.reverse ()
+            return Path (self.context, path[j:i + 1] + segment)
 
 class AlgoThread (threading.Thread):