(gdb) bt
#0  0x00007ffffeb01bbc in _int_malloc (av=av@entry=0x7ffffee44b20 <main_arena>, bytes=bytes@entry=16) at malloc.c:3353
#1  0x00007ffffeb04184 in __GI___libc_malloc (bytes=16) at malloc.c:2913
#2  0x00007fffff0fde78 in operator new(unsigned long) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#3  0x0000000000404d1c in __gnu_cxx::new_allocator<std::__detail::_Hash_node_base*>::allocate (this=0x7fffff7df167, __n=2)
    at /usr/include/c++/5/ext/new_allocator.h:104
#4  0x000000000040474f in std::allocator_traits<std::allocator<std::__detail::_Hash_node_base*> >::allocate (__a=..., __n=2)
    at /usr/include/c++/5/bits/alloc_traits.h:491
#5  0x0000000000403e2d in std::__detail::_Hashtable_alloc<std::allocator<std::__detail::_Hash_node<int, false> > >::_M_allocate_buckets (this=0x7fffff7df300, __n=2)
    at /usr/include/c++/5/bits/hashtable_policy.h:1996
#6  0x0000000000403187 in std::_Hashtable<int, int, std::allocator<int>, std::__detail::_Identity, std::equal_to<int>, std::hash<int>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, true, true> >::_M_allocate_buckets (
    this=0x7fffff7df300, __n=2) at /usr/include/c++/5/bits/hashtable.h:347
#7  0x00000000004020f1 in std::_Hashtable<int, int, std::allocator<int>, std::__detail::_Identity, std::equal_to<int>, std::hash<int>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false, true, true> >::operator= (this=0x7fffff7df300,
    __ht=...) at /usr/include/c++/5/bits/hashtable.h:906
#8  0x000000000040197b in std::unordered_set<int, std::hash<int>, std::equal_to<int>, std::allocator<int> >::operator= (this=0x7fffff7df300)
    at /usr/include/c++/5/bits/unordered_set.h:93
#9  0x000000000040136e in minNodeCover (start=2, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:81
#10 0x000000000040115d in minNodeCover (start=1, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:61
#11 0x00000000004013b7 in minNodeCover (start=3, S=std::unordered_set with 0 elements) at mincover.cpp:83
#12 0x0000000000401440 in minNodeCover (start=2, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:90
#13 0x000000000040115d in minNodeCover (start=1, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:61
#14 0x00000000004013b7 in minNodeCover (start=3, S=std::unordered_set with 0 elements) at mincover.cpp:83
#15 0x0000000000401440 in minNodeCover (start=2, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:90
#16 0x000000000040115d in minNodeCover (start=1, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:61
#17 0x00000000004013b7 in minNodeCover (start=3, S=std::unordered_set with 0 elements) at mincover.cpp:83
#18 0x0000000000401440 in minNodeCover (start=2, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:90
#19 0x000000000040115d in minNodeCover (start=1, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:61
#20 0x00000000004013b7 in minNodeCover (start=3, S=std::unordered_set with 0 elements) at mincover.cpp:83
#21 0x0000000000401440 in minNodeCover (start=2, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:90
#22 0x000000000040115d in minNodeCover (start=1, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:61
#23 0x00000000004013b7 in minNodeCover (start=3, S=std::unordered_set with 0 elements) at mincover.cpp:83
#24 0x0000000000401440 in minNodeCover (start=2, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:90
#25 0x000000000040115d in minNodeCover (start=1, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:61
#26 0x00000000004013b7 in minNodeCover (start=3, S=std::unordered_set with 0 elements) at mincover.cpp:83
#27 0x0000000000401440 in minNodeCover (start=2, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:90
#28 0x000000000040115d in minNodeCover (start=1, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:61
#29 0x00000000004013b7 in minNodeCover (start=3, S=std::unordered_set with 0 elements) at mincover.cpp:83
#30 0x0000000000401440 in minNodeCover (start=2, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:90
#31 0x000000000040115d in minNodeCover (start=1, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:61
#32 0x00000000004013b7 in minNodeCover (start=3, S=std::unordered_set with 0 elements) at mincover.cpp:83
#33 0x0000000000401440 in minNodeCover (start=2, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:90
#34 0x000000000040115d in minNodeCover (start=1, S=std::unordered_set with 1 elements = {...}) at mincover.cpp:61