Language: C++

#include<iostream>
#include<cstring>
#include<cstdio>
#include<vector>
#include<algorithm>

using namespace std;

#define LL long long
#define fgx cerr<<"--------------"<<endl;
#define dgx cerr<<"=============="<<endl;

inline int read(){
	int x=0,f=1;char c=getchar();
	for(;!isdigit(c);c=getchar()) if(c=='-') f=-1;
	for(;isdigit(c);c=getchar()) x=x*10+c-'0';
	return x*f;
}
const int MAXN = 200010;
const LL INF = 2147483600;

struct data{
	LL id,val;
}a[MAXN+1]; LL N;
bool cmpval(data a,data b){
	return a.val>b.val;
}
LL Node[MAXN<<1],Next[MAXN<<1],Root[MAXN+1],cnt;
inline void insert(LL u,LL v){
	Node[++cnt]=v; Next[cnt]=Root[u]; Root[u]=cnt; return ;
} LL sz[MAXN+1],f[MAXN+1],b[MAXN+1];
inline void dfs(LL k,LL Fa){
	sz[k]=1;
	for(LL x=Root[k];x;x=Next[x]){
		LL v=Node[x]; if(v==Fa) continue;
		dfs(v,k); sz[k]+=sz[v]; f[1]+=sz[v];
	} return ;
}
inline void dfs2(LL k,LL Fa){
	if(f[k]!=b[k]){ puts("-1"); exit(0); }
	for(LL x=Root[k];x;x=Next[x]){
		LL v=Node[x]; if(v==Node[x]) continue;
		f[v]=f[k]+N-2*sz[v]; dfs2(v,k);
	} return ;
} LL s1[MAXN+1],s2[MAXN+1],top;

int main(){
	//freopen(".in","r",stdin);
	//freopen(".out","w",stdout);
	N=read();
	for(LL i=1;i<=N;i++){
		a[i].id=i; a[i].val=read(); b[i]=a[i].val;
	} sort(a+1,a+N+1,cmpval);
	for(LL i=1;i<=N;i++) sz[i]=1;
	for(LL i=1;i<N;i++){
		LL val=a[i].val-N+2*sz[i]; 
		LL l=i+1,r=N,pos=-1;
		while(l<=r){
			LL mid=(l+r)>>1;
			if(a[mid].val>=val) pos=mid,l=mid+1;
			else r=mid-1;
		} if(pos==-1||a[pos].val!=val){
			puts("-1"); return 0;
		} sz[pos]+=sz[i];
		s1[++top]=a[i].id; s2[top]=a[pos].id;
		insert(a[i].id,a[pos].id);
		insert(a[pos].id,a[i].id);
		//sz=N+a[fa]-a[i].val
	} dfs(1,0); dfs2(1,0);
	for(LL i=1;i<=top;i++) printf("%lld %lld\n",s1[i],s2[i]); 
	return 0;
}




Compiler output:
a.cc:25:13: error: reference to 'data' is ambiguous
   25 | bool cmpval(data a,data b){
      |             ^~~~
In file included from /usr/include/c++/14/string:53,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/range_access.h:344:5: note: candidates are: 'template<class _Tp> constexpr const _Tp* std::data(initializer_list<_Tp>)'
  344 |     data(initializer_list<_Tp> __il) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:334:5: note:                 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::data(_Tp (&)[_Nm])'
  334 |     data(_Tp (&__array)[_Nm]) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:323:5: note:                 'template<class _Container> constexpr decltype (__cont.data()) std::data(const _Container&)'
  323 |     data(const _Container& __cont) noexcept(noexcept(__cont.data()))
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:312:5: note:                 'template<class _Container> constexpr decltype (__cont.data()) std::data(_Container&)'
  312 |     data(_Container& __cont) noexcept(noexcept(__cont.data()))
      |     ^~~~
a.cc:22:8: note:                 'struct data'
   22 | struct data{
      |        ^~~~
a.cc:25:20: error: reference to 'data' is ambiguous
   25 | bool cmpval(data a,data b){
      |                    ^~~~
/usr/include/c++/14/bits/range_access.h:344:5: note: candidates are: 'template<class _Tp> constexpr const _Tp* std::data(initializer_list<_Tp>)'
  344 |     data(initializer_list<_Tp> __il) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:334:5: note:                 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::data(_Tp (&)[_Nm])'
  334 |     data(_Tp (&__array)[_Nm]) noexcept
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:323:5: note:                 'template<class _Container> constexpr decltype (__cont.data()) std::data(const _Container&)'
  323 |     data(const _Container& __cont) noexcept(noexcept(__cont.data()))
      |     ^~~~
/usr/include/c++/14/bits/range_access.h:312:5: note:                 'template<class _Container> constexpr decltype (__cont.data()) std::data(_Container&)'
  312 |     data(_Container& __cont) noexcept(noexcept(__cont.data()))
      |     ^~~~
a.cc:22:8: note:                 'struct data'
   22 | struct data{
      |        ^~~~
a.cc:25:26: error: expression list treated as compound expression in initializer [-fpermissive]
   25 | bool cmpval(data a,data b){
      |                          ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:71,
                 from /usr/include/c++/14/string:51:
/usr/include/c++/14/bits/predefined_ops.h: In instantiation of 'constexpr bool __gnu_cxx::__ops::_Iter_comp_iter<_Compare>::operator()(_Iterator1, _Iterator2) [with _Iterator1 = data*; _Iterator2 = data*; _Compare = bool]':
/usr/include/c++/14/bits/stl_algo.h:1777:14:   required from 'void std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
 1777 |           if (__comp(__i, __first))
      |               ~~~~~~^~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1817:25:   required from 'void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
 1817 |           std::__insertion_sort(__first, __first + int(_S_threshold), __comp);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1908:31:   required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
 1908 |           std::__final_insertion_sort(__first, __last, __comp);
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:4805:18:   required from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = data*; _Compare = bool]'
 4805 |       std::__sort(__first, __last, __gnu_cxx::__ops::__iter_comp_iter(__comp));
      |       ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:53:8:   required from here
   53 |         } sort(a+1,a+N+1,cmpval);
      |           ~~~~^~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/predefined_ops.h:158:30: error: expression cannot be used as a function
  158 |         { return bool(_M_comp(*__it1, *__it2)); }
      |                       ~~~~~~~^~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/predefined_ops.h: In instantiation of 'bool __gnu_cxx::__ops::_Val_comp_iter<_Compare>::operator()(_Value&, _Iterator) [with _Value = data; _Iterator = data*; _Compare = bool]':
/usr/include/c++/14/bits/stl_algo.h:1757:20:   required from 'void std::__unguarded_linear_insert(_RandomAccessIterator, _Compare) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Val_comp_iter<bool>]'
 1757 |       while (__comp(__val, __next))
      |              ~~~~~~^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1785:36:   required from 'void std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
 1785 |             std::__unguarded_linear_insert(__i,
      |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
 1786 |                                 __gnu_cxx::__ops::__val_comp_iter(__comp));
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1817:25:   required from 'void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
 1817 |           std::__insertion_sort(__first, __first + int(_S_threshold), __comp);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1908:31:   required from 'void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
 1908 |           std::__final_insertion_sort(__first, __last, __comp);
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:4805:18:   required from 'void std::sort(_RAIter, _RAIter, _Compare) [with _RAIter = data*; _Compare = bool]'
 4805 |       std::__sort(__first, __last, __gnu_cxx::__ops::__iter_comp_iter(__comp));
      |       ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:53:8:   required from here
   53 |         } sort(a+1,a+N+1,cmpval);
      |           ~~~~^~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/predefined_ops.h:240:30: error: expression cannot be used as a function
  240 |         { return bool(_M_comp(__val, *__it)); }
      |                       ~~~~~~~^~~~~~~~~~~~~~
/usr/include/c++/14/bits/predefined_ops.h: In instantiation of 'bool __gnu_cxx::__ops::_Iter_comp_val<_Compare>::operator()(_Iterator, _Value&) [with _Iterator = data*; _Value = data; _Compare = bool]':
/usr/include/c++/14/bits/stl_heap.h:140:48:   required from 'void std::__push_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare&) [with _RandomAccessIterator = data*; _Distance = long int; _Tp = data; _Compare = __gnu_cxx::__ops::_Iter_comp_val<bool>]'
  140 |       while (__holeIndex > __topIndex && __comp(__first + __parent, __value))
      |                                          ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_heap.h:247:23:   required from 'void std::__adjust_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = data*; _Distance = long int; _Tp = data; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
  247 |       std::__push_heap(__first, __holeIndex, __topIndex,
      |       ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  248 |                        _GLIBCXX_MOVE(__value), __cmp);
      |                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_heap.h:356:22:   required from 'void std::__make_heap(_RandomAccessIterator, _RandomAccessIterator, _Compare&) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
  356 |           std::__adjust_heap(__first, __parent, __len, _GLIBCXX_MOVE(__value),
      |           ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  357 |                              __comp);
      |                              ~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1593:23:   required from 'void std::__heap_select(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
 1593 |       std::__make_heap(__first, __middle, __comp);
      |       ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1868:25:   required from 'void std::__partial_sort(_RandomAccessIterator, _RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = data*; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
 1868 |       std::__heap_select(__first, __middle, __last, __comp);
      |       ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1884:27:   required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare) [with _RandomAccessIterator = data*; _Size = long int; _Compare = __gnu_cxx::__ops::_Iter_comp_iter<bool>]'
 1884 |               std::__partial_sort(__first, __last, __last, __comp);
      |               ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:1905:25:   requi