Language: C++

#include<iostream>
#include<set>
#include<deque>
#include<utility>
#include<algorithm>
#include<stack>
#include<vector>
#include<string>

using namespace std;

bool used[8][8][8][8][8][8][8][8];

inline bool judge(vector<int> ar){

    for(int i=0;i<ar.size();i++){
	if (ar[i] != i) return false;
    }
    return true;
}

inline int findzero(vector<int> ar){
    for(int i=0;i<8;i++){
	if(ar[i] == 0) return i;
    }
    return 0;
}

int main(){

    vector<int> ar(8);
//    set< vector<int> > memo1;
//   set< vector<int> > memo2;
    deque< vector<int> > next;
    deque< vector<int> > rec;
    int d[] = {-4,-1,1,4};
    int zero,nextzero;
    bool endflag=false,flag;
    int res; 
    while(true){
	memset(used,0,sizeof(used));
	res = 0;
	flag = false;
	for(int i=0;i<8;i++){
	    if((cin >> ar[i])==0){
		endflag = true;
		break;
	    }
	    if(ar[i] == 0) zero = i;
	}
	if(endflag) break;
	next.push_back(ar);
	if(judge(ar)){ 
	    flag = true; 
	    cout << res << endl;
	}
	while(!flag){
	    res++;
	    while(!next.empty()){
		ar = next.front();
		used[ar[0]][ar[1]][ar[2]][ar[3]][ar[4]][ar[5]][ar[6]][ar[7]] = true;
		zero = findzero(ar);
		next.pop_front();
		for(int i=0;i<4;i++){
		    nextzero = zero + d[i];
		    if(nextzero>-1&&nextzero<8){
			if(zero == 3 && i==2) continue;
			else if(zero == 4 && i == 1) continue;
		       swap(ar[nextzero],ar[zero]);
		       if(judge(ar)){
			   flag = true;
			   cout << res << endl;
			   break;
		       }
			if(!used[ar[0]][ar[1]][ar[2]][ar[3]][ar[4]][ar[5]][ar[6]][ar[7]]){
			    rec.push_back(ar);
			}
		       swap(ar[nextzero],ar[zero]);
		    }
		}
		if(flag) break;
	    }
	    swap(next,rec);
	}
	if(flag){
	    next.clear();
	    rec.clear();
	}

    }
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:41:9: error: 'memset' was not declared in this scope
   41 |         memset(used,0,sizeof(used));
      |         ^~~~~~
a.cc:8:1: note: 'memset' is defined in header '<cstring>'; this is probably fixable by adding '#include <cstring>'
    7 | #include<vector>
  +++ |+#include <cstring>
    8 | #include<string>
a.cc:45:30: error: no match for 'operator==' (operand types are 'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} and 'int')
   45 |             if((cin >> ar[i])==0){
      |                ~~~~~~~~~~~~~~^~~
      |                     |          |
      |                     |          int
      |                     std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}
a.cc:45:30: note: candidate: 'operator==(int, int)' (built-in)
   45 |             if((cin >> ar[i])==0){
      |                ~~~~~~~~~~~~~~^~~
a.cc:45:30: note:   no known conversion for argument 1 from 'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} to 'int'
In file included from /usr/include/c++/14/iosfwd:42,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/postypes.h:192:5: note: candidate: 'template<class _StateT> bool std::operator==(const fpos<_StateT>&, const fpos<_StateT>&)'
  192 |     operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:192:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} is not derived from 'const std::fpos<_StateT>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
In file included from /usr/include/c++/14/string:43,
                 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:
/usr/include/c++/14/bits/allocator.h:235:5: note: candidate: 'template<class _T1, class _T2> bool std::operator==(const allocator<_CharT>&, const allocator<_T2>&)'
  235 |     operator==(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:235:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} is not derived from 'const std::allocator<_CharT>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
In file included from /usr/include/c++/14/string:48:
/usr/include/c++/14/bits/stl_iterator.h:441:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  441 |     operator==(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:441:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
/usr/include/c++/14/bits/stl_iterator.h:486:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  486 |     operator==(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1667 |     operator==(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1737 |     operator==(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51:
/usr/include/c++/14/bits/stl_pair.h:1033:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator==(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1033 |     operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1033:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} is not derived from 'const std::pair<_T1, _T2>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:629:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  629 |     operator==(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:629:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
/usr/include/c++/14/string_view:637:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  637 |     operator==(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:637:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
/usr/include/c++/14/string_view:644:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  644 |     operator==(__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:644:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'int'
   45 |             if((cin >> ar[i])==0){
      |                                ^
/usr/include/c++/14/bits/basic_string.h:3755:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3755 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3755:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
/usr/include/c++/14/bits/basic_string.h:3772:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3772 |     operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3772:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
/usr/include/c++/14/bits/basic_string.h:3819:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator==(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3819 |     operator==(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3819:5: note:   template argument deduction/substitution failed:
a.cc:45:32: note:   mismatched types 'const _CharT*' and 'std::basic_istream<char>'
   45 |             if((cin >> ar[i])==0){
      |                                ^
In file included from /usr/include/c++/14/bits/memory_resource.h:47,
                 from /usr/include/c++/14/string:68:
/usr/include/c++/14/tuple:2558:5: note: candidate: 'template<class ... _TElements, class ... _UElements> constexpr bool std::operator==(const tuple<_UTypes ...>&, const tuple<_Elements ...>&)'
 2558 |     operator==(const tuple<_TElements...>& __t,
      |     ^~~~~~~~
/usr/include/c++/14/tuple:25