Use FIFO queue for S-vertices

python/mwmatching.py

@@ -6,6 +6,7 @@ from __future__ import annotations
 
 import sys
 import math
+import collections
 from collections.abc import Sequence
 from typing import NamedTuple, Optional
 
@@ -545,9 +546,8 @@ class _MatchingContext:
         # between "x" and any S-vertex, or -1 if no such edge has been found.
         self.vertex_best_edge: list[int] = num_vertex * [-1]
 
-        # "queue" is a list of S-vertices that must be scanned.
-        # We call it a queue, but it is actually a stack.
-        self.queue: list[int] = []
+        # Queue of S-vertices to be scanned.
+        self.queue: collections.deque[int] = collections.deque()
 
     def edge_slack_2x(self, e: int) -> int|float:
         """Return 2 times the slack of the edge with index "e".
@@ -1361,7 +1361,7 @@ class _MatchingContext:
         while self.queue:
 
             # Take a vertex from the queue.
-            x = self.queue.pop()
+            x = self.queue.popleft()
 
             # Double-check that "x" is an S-vertex.
             bx = self.vertex_top_blossom[x]

python/test_mwmatching.py

@@ -194,15 +194,15 @@ class TestMaximumWeightMatching(unittest.TestCase):
     def test46_expand_unlabeled_blossom(self):
         """expand blossom before assigning label T"""
         #
-        #                5--[2]--3--[4]
+        #              3--[1]
         #             /    |
-        #    [0]--5--[1]     5
+        #  [2]--1--[4]     7
         #             \    |
-        #                5--[3]--3--[5]
+        #              5--[3]--5--[5]
         #
-        self.assertEqual(
-            mwm([(0,1,5), (1,2,5), (1,3,5), (2,3,5), (2,4,3), (3,5,3)]),
-            [(0,1), (2,4), (3,5)])
+        self.assertIn(
+            mwm([(1,3,7), (1,4,3), (2,4,1), (3,4,5), (3,5,5)]),
+            ([(1,3), (2,4)], [(1,4), (3,5)]))
 
     def test47_expand_unlabeled_outer(self):
         """expand outer blossom before assigning label T"""
@@ -217,6 +217,19 @@ class TestMaximumWeightMatching(unittest.TestCase):
             mwm([(1,2,15), (1,3,10), (1,4,11), (1,6,17), (2,5,12), (2,6,8), (5,7,15), (6,7,7)]),
             [(1,4), (2,6), (5,7)])
 
+    def test48_expand_unlabeled_nested(self):
+        """expand nested blossom before assigning label T"""
+        #
+        #  [5]--11--[1]--11     14--[3]
+        #            |     \   /     |
+        #           12      [4]     14
+        #            |     /   \     |
+        #  [6]--11--[2]--12     11--[7]
+        #
+        self.assertEqual(
+            mwm([(1,2,12), (1,4,11), (1,5,11), (2,4,12), (2,6,11), (3,4,14), (3,7,14), (4,7,11)]),
+            [(1,5), (2,4), (3,7)])
+
     def test_fail_bad_input(self):
         """bad input values"""
         with self.assertRaises(TypeError):
@@ -315,6 +328,10 @@ class TestCornerCases(unittest.TestCase):
         pairs = mwm([(0,2,13), (1,2,11), (2,3,39), (2,4,17), (3,4,35)])
         self.assertEqual(pairs, [(0,2), (3,4)])
 
+    def test17(self):
+        pairs = mwm([(0,1,48), (0,2,44), (0,4,48), (1,4,36), (3,4,31)])
+        self.assertEqual(pairs, [(0,2), (1,4)])
+
 
 class TestAdjustWeightForMaxCardinality(unittest.TestCase):
     """Test adjust_weights_for_maximum_cardinality_matching() function."""