From 4fd001e8bf5ec293913531ba56a891181edf8f45 Mon Sep 17 00:00:00 2001
From: Jonathan Kliem <jonathan.kliem@fu-berlin.de>
Date: Mon, 28 Dec 2020 19:38:45 +0100
Subject: [PATCH] reuse queue

---
 src/sage/graphs/base/c_graph.pyx | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/src/sage/graphs/base/c_graph.pyx b/src/sage/graphs/base/c_graph.pyx
index 10c6dd8b113..72284b1d35f 100644
--- a/src/sage/graphs/base/c_graph.pyx
+++ b/src/sage/graphs/base/c_graph.pyx
@@ -46,7 +46,7 @@ method :meth:`realloc <sage.graphs.base.c_graph.CGraph.realloc>`.
 from sage.data_structures.bitset_base cimport *
 from sage.rings.integer cimport Integer
 from sage.arith.long cimport pyobject_to_long
-from libcpp.queue cimport priority_queue
+from libcpp.queue cimport priority_queue, queue
 from libcpp.pair cimport pair
 from sage.rings.integer_ring import ZZ
 from cysignals.memory cimport check_allocarray, sig_free
@@ -4716,9 +4716,7 @@ cdef class Search_iterator:
     cdef CGraphBackend graph
     cdef int direction
     cdef list stack
-    cdef int* queue
-    cdef int queue_begin
-    cdef int queue_end
+    cdef queue[int] fifo
     cdef int n
     cdef bitset_t seen
     cdef bint test_out
@@ -4795,10 +4793,7 @@ cdef class Search_iterator:
             raise LookupError("vertex ({0}) is not a vertex of the graph".format(repr(v)))
 
         if direction == 0:
-            self.queue = <int*>sig_malloc(self.n * sizeof(int))
-            self.queue_begin = 0
-            self.queue_end = 0
-            self.queue[0] = v_id
+            self.fifo.push(v_id)
             bitset_add(self.seen, v_id)
         else:
             self.stack = [v_id]
@@ -4816,8 +4811,6 @@ cdef class Search_iterator:
         r"""
         Freeing the memory
         """
-        if self.direction == 0:
-            sig_free(self.queue)
         bitset_free(self.seen)
 
     def __iter__(self):
@@ -4849,9 +4842,9 @@ cdef class Search_iterator:
         cdef int l
         cdef CGraph cg = self.graph.cg()
 
-        if self.queue_begin <= self.queue_end:
-            v_int = self.queue[self.queue_begin]
-            self.queue_begin += 1
+        while not self.fifo.empty():
+            v_int = self.fifo.front()
+            self.fifo.pop()
             value = self.graph.vertex_label(v_int)
 
             if self.test_out:
@@ -4859,16 +4852,14 @@ cdef class Search_iterator:
                 while w_int != -1:
                     if bitset_not_in(self.seen, w_int):
                         bitset_add(self.seen, w_int)
-                        self.queue_end += 1
-                        self.queue[self.queue_end] = w_int
+                        self.fifo.push(w_int)
                     w_int = cg.next_out_neighbor_unsafe(v_int, w_int, &l)
             if self.test_in:
                 w_int = cg.next_in_neighbor_unsafe(v_int, -1, &l)
                 while w_int != -1:
                     if bitset_not_in(self.seen, w_int):
                         bitset_add(self.seen, w_int)
-                        self.queue_end += 1
-                        self.queue[self.queue_end] = w_int
+                        self.fifo.push(w_int)
                     w_int = cg.next_in_neighbor_unsafe(v_int, w_int, &l)
 
         else: