sagemathgh-40930: Fix order of endpoint of edges in yen_shortest_paths
    
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Fixes sagemath#40878. Especially fix the order of endpoint of edges of the
result of yen_k_shortest_path function.

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URL: sagemath#40930
Reported by: Yuta Inoue
Reviewer(s): David Coudert

Author: Release Manager

src/sage/graphs/path_enumeration.pyx

@@ -417,16 +417,16 @@ def shortest_simple_paths(self, source, target, weight_function=None,
          [1, 2, 3, 8, 9, 11, 6],
          [1, 2, 3, 4, 5, 6]]
         sage: list(g.shortest_simple_paths(1, 6, report_edges=True, labels=True, by_weight=True))
-        [[(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 7, 3), (6, 7, 4)],
-         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (6, 9, 2)],
-         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 10, 7), (6, 10, 2)],
-         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 11, 10), (6, 11, 8)],
+        [[(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 7, 3), (7, 6, 4)],
+         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 6, 2)],
+         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 10, 7), (10, 6, 2)],
+         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 11, 10), (11, 6, 8)],
          [(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 5, 2), (5, 6, 100)]]
         sage: list(g.shortest_simple_paths(1, 6, report_edges=True, labels=True, by_weight=True, report_weight=True))
-        [(10, [(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 7, 3), (6, 7, 4)]),
-         (11, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (6, 9, 2)]),
-         (18, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 10, 7), (6, 10, 2)]),
-         (27, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 11, 10), (6, 11, 8)]),
+        [(10, [(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 7, 3), (7, 6, 4)]),
+         (11, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 6, 2)]),
+         (18, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 10, 7), (10, 6, 2)]),
+         (27, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 11, 10), (11, 6, 8)]),
          (105, [(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 5, 2), (5, 6, 100)])]
         sage: list(g.shortest_simple_paths(1, 6, algorithm='Yen'))
         [[1, 2, 3, 4, 5, 6],
@@ -720,16 +720,16 @@ def yen_k_shortest_simple_paths(self, source, target, weight_function=None,
          [1, 2, 3, 8, 9, 11, 6],
          [1, 2, 3, 4, 5, 6]]
         sage: list(yen_k_shortest_simple_paths(g, 1, 6, report_edges=True, labels=True, by_weight=True))
-        [[(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 7, 3), (6, 7, 4)],
-         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (6, 9, 2)],
-         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 10, 7), (6, 10, 2)],
-         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 11, 10), (6, 11, 8)],
+        [[(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 7, 3), (7, 6, 4)],
+         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 6, 2)],
+         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 10, 7), (10, 6, 2)],
+         [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 11, 10), (11, 6, 8)],
          [(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 5, 2), (5, 6, 100)]]
         sage: list(yen_k_shortest_simple_paths(g, 1, 6, report_edges=True, labels=True, by_weight=True, report_weight=True))
-        [(10, [(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 7, 3), (6, 7, 4)]),
-         (11, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (6, 9, 2)]),
-         (18, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 10, 7), (6, 10, 2)]),
-         (27, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 11, 10), (6, 11, 8)]),
+        [(10, [(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 7, 3), (7, 6, 4)]),
+         (11, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 6, 2)]),
+         (18, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 10, 7), (10, 6, 2)]),
+         (27, [(1, 2, 1), (2, 3, 1), (3, 8, 5), (8, 9, 2), (9, 11, 10), (11, 6, 8)]),
          (105, [(1, 2, 1), (2, 3, 1), (3, 4, 1), (4, 5, 2), (5, 6, 100)])]
         sage: list(yen_k_shortest_simple_paths(g, 1, 6))
         [[1, 2, 3, 4, 5, 6],
@@ -813,8 +813,8 @@ def yen_k_shortest_simple_paths(self, source, target, weight_function=None,
     if report_edges and labels:
         edge_labels = {(e[0], e[1]): e for e in G.edge_iterator()}
         if not G.is_directed():
-            for u, v in G.edge_iterator(labels=False):
-                edge_labels[v, u] = edge_labels[u, v]
+            for u, v, l in G.edge_iterator(labels=True):
+                edge_labels[v, u] = (v, u, l)
 
     # heap data structure containing the candidate paths
     cdef priority_queue[pair[double, pair[int, int]]] heap_sorted_paths