/in/foo.cc: In function 'void Dijkstra(int)':
/in/foo.cc:18:4: error: reference to 'prev' is ambiguous
    prev[i]=-1;
    ^~~~
/in/foo.cc:8:5: note: candidates are: int prev [110]
 int prev[maxn]={0};
     ^~~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/7/algorithm:61,
                 from /in/foo.cc:2:
/usr/include/c++/7/bits/stl_iterator_base_funcs.h:220:5: note:                 template<class _BidirectionalIterator> _BidirectionalIterator std::prev(_BidirectionalIterator, typename std::iterator_traits<_Iter>::difference_type)
     prev(_BidirectionalIterator __x, typename
     ^~~~
/in/foo.cc:20:4: error: reference to 'prev' is ambiguous
    prev[i]=sp;
    ^~~~
/in/foo.cc:8:5: note: candidates are: int prev [110]
 int prev[maxn]={0};
     ^~~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/7/algorithm:61,
                 from /in/foo.cc:2:
/usr/include/c++/7/bits/stl_iterator_base_funcs.h:220:5: note:                 template<class _BidirectionalIterator> _BidirectionalIterator std::prev(_BidirectionalIterator, typename std::iterator_traits<_Iter>::difference_type)
     prev(_BidirectionalIterator __x, typename
     ^~~~
/in/foo.cc:38:6: error: reference to 'prev' is ambiguous
      prev[j]=u;
      ^~~~
/in/foo.cc:8:5: note: candidates are: int prev [110]
 int prev[maxn]={0};
     ^~~~
In file included from /usr/include/c++/7/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/7/algorithm:61,
                 from /in/foo.cc:2:
/usr/include/c++/7/bits/stl_iterator_base_funcs.h:220:5: note:                 template<class _BidirectionalIterator> _BidirectionalIterator std::prev(_BidirectionalIterator, typename std::iterator_traits<_Iter>::difference_type)
     prev(_BidirectionalIterator __x, typename
     ^~~~