/in/foo.cc: In function 'bool spfa()':
/in/foo.cc:40:13: error: reference to 'prev' is ambiguous
             prev[e[i].to] = u;
             ^~~~
/in/foo.cc:11:23: note: candidates are: int prev [405]
 int head[N], pree[N], prev[N], t[N], vis[N], l[N], p[N];
                       ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/deque:60,
                 from /usr/include/c++/6/queue:60,
                 from /in/foo.cc:3:
/usr/include/c++/6/bits/stl_iterator_base_funcs.h:217:5: note:                 template<class _BidirectionalIterator> _BidirectionalIterator std::prev(_BidirectionalIterator, typename std::iterator_traits<_Iter>::difference_type)
     prev(_BidirectionalIterator __x, typename
     ^~~~
/in/foo.cc: In function 'long long int Edmonds_Karp()':
/in/foo.cc:61:19: error: reference to 'prev' is ambiguous
             now = prev[now];
                   ^~~~
/in/foo.cc:11:23: note: candidates are: int prev [405]
 int head[N], pree[N], prev[N], t[N], vis[N], l[N], p[N];
                       ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/deque:60,
                 from /usr/include/c++/6/queue:60,
                 from /in/foo.cc:3:
/usr/include/c++/6/bits/stl_iterator_base_funcs.h:217:5: note:                 template<class _BidirectionalIterator> _BidirectionalIterator std::prev(_BidirectionalIterator, typename std::iterator_traits<_Iter>::difference_type)
     prev(_BidirectionalIterator __x, typename
     ^~~~
/in/foo.cc:68:19: error: reference to 'prev' is ambiguous
             now = prev[now];
                   ^~~~
/in/foo.cc:11:23: note: candidates are: int prev [405]
 int head[N], pree[N], prev[N], t[N], vis[N], l[N], p[N];
                       ^~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/6/deque:60,
                 from /usr/include/c++/6/queue:60,
                 from /in/foo.cc:3:
/usr/include/c++/6/bits/stl_iterator_base_funcs.h:217:5: note:                 template<class _BidirectionalIterator> _BidirectionalIterator std::prev(_BidirectionalIterator, typename std::iterator_traits<_Iter>::difference_type)
     prev(_BidirectionalIterator __x, typename
     ^~~~