Language: C++

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                          /*****************main*****************/
/*OJ:
  ProblemID:
  Date:
*/
#include<bits/stdc++.h>
#define mp make_pair
#define pb push_back
#define all(n) (n).begin,(n).end
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<pair<int,int>,int> piii;
typedef vector<int> vi;
const int INF=1e9+7;
/*_____main part_____*/
vector<int> v[500000];
int n,begin,ans;
string s;
int dp[500005];
bool check;
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	/*freopen("input.txt","r",stdin);
	freopen("output.txt","w",stdout);*/
	cin>>n>>s;
	for(int i=0;i<=s.length() ;i++)
	{
		//cout<<i<<endl;
		if(s[i]=='0' and check)
		{
			check=false;
			v[begin].push_back(i-1);
			if(s[i-2]=='1')
			v[begin].push_back(i-2); 
			if(s[i+1]=='1' and i+1<s.length())
			{
				check=true;
				begin=i-1;
				i+=1;
				continue;
			 } 
		}
		if(check and i==s.length() )
		{
			//cout<<"OK";
			v[begin].push_back(i-1); 	
			break;
		}
		if(!check and s[i]=='1' and s[i+1]=='0' and s[i+2]=='1')
		{
			check=true;
			begin=i;
			i+=2;
			continue;
		}
	}
	check=false;
	for(int i=s.length() -1;i>=-1;i--)
	{
		if(s[i]=='0' and check)
		{
			check=false;
			v[i+1].push_back(begin);
			if(s[i+2]=='1')
			v[i+2].push_back(begin); 
			if(s[i-1]=='1' and i-1>0)
			{
				check=true;
				begin=i+1;
				i--;
				continue;
			}
		}
		if(check and i==-1)
		{
			//cout<<"OK";
			v[0].push_back(begin);
			break; 
		}
		if(!check and s[i]=='1' and s[i-1]=='0' and s[i-2]=='1')
		{
			check=true;
			begin=i;
			i-=2;
			continue;
		}
	}
	dp[0]=0;
	for(int i=0;i<s.length() ;i++)
	{
		if(dp[i]==0 and i!=0)
		dp[i]=dp[i-1];
		for(int j=0;j<v[i].size() ;j++)
		{
			dp[v[i][j]]=max(dp[v[i][j]],dp[max(i-1,0)]+v[i][j]-i-1);
			ans=max(ans,dp[v[i][j]]);
		}
	}
	cout<<ans;
	return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:97:27: error: reference to 'begin' is ambiguous
   97 |                         v[begin].push_back(i-1);
      |                           ^~~~~
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166,
                 from a.cc:67:
/usr/include/c++/14/valarray:1238:5: note: candidates are: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227:5: note:                 'template<class _Tp> _Tp* std::begin(valarray<_Tp>&)'
 1227 |     begin(valarray<_Tp>& __va) noexcept
      |     ^~~~~
In file included from /usr/include/c++/14/string:53,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/range_access.h:95:5: note:                 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
   95 |     begin(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&)'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:52:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&)'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
In file included from /usr/include/c++/14/bits/algorithmfwd.h:39,
                 from /usr/include/c++/14/bits/stl_algo.h:59,
                 from /usr/include/c++/14/algorithm:61,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/initializer_list:88:5: note:                 'template<class _Tp> constexpr const _Tp* std::begin(initializer_list<_Tp>)'
   88 |     begin(initializer_list<_Tp> __ils) noexcept
      |     ^~~~~
a.cc:79:7: note:                 'int begin'
   79 | int n,begin,ans;
      |       ^~~~~
a.cc:99:27: error: reference to 'begin' is ambiguous
   99 |                         v[begin].push_back(i-2);
      |                           ^~~~~
/usr/include/c++/14/valarray:1238:5: note: candidates are: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227:5: note:                 'template<class _Tp> _Tp* std::begin(valarray<_Tp>&)'
 1227 |     begin(valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note:                 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
   95 |     begin(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&)'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:52:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&)'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/initializer_list:88:5: note:                 'template<class _Tp> constexpr const _Tp* std::begin(initializer_list<_Tp>)'
   88 |     begin(initializer_list<_Tp> __ils) noexcept
      |     ^~~~~
a.cc:79:7: note:                 'int begin'
   79 | int n,begin,ans;
      |       ^~~~~
a.cc:103:33: error: reference to 'begin' is ambiguous
  103 |                                 begin=i-1;
      |                                 ^~~~~
/usr/include/c++/14/valarray:1238:5: note: candidates are: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227:5: note:                 'template<class _Tp> _Tp* std::begin(valarray<_Tp>&)'
 1227 |     begin(valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note:                 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
   95 |     begin(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&)'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:52:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&)'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/initializer_list:88:5: note:                 'template<class _Tp> constexpr const _Tp* std::begin(initializer_list<_Tp>)'
   88 |     begin(initializer_list<_Tp> __ils) noexcept
      |     ^~~~~
a.cc:79:7: note:                 'int begin'
   79 | int n,begin,ans;
      |       ^~~~~
a.cc:111:27: error: reference to 'begin' is ambiguous
  111 |                         v[begin].push_back(i-1);
      |                           ^~~~~
/usr/include/c++/14/valarray:1238:5: note: candidates are: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227:5: note:                 'template<class _Tp> _Tp* std::begin(valarray<_Tp>&)'
 1227 |     begin(valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note:                 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
   95 |     begin(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&)'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:52:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&)'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/initializer_list:88:5: note:                 'template<class _Tp> constexpr const _Tp* std::begin(initializer_list<_Tp>)'
   88 |     begin(initializer_list<_Tp> __ils) noexcept
      |     ^~~~~
a.cc:79:7: note:                 'int begin'
   79 | int n,begin,ans;
      |       ^~~~~
a.cc:117:25: error: reference to 'begin' is ambiguous
  117 |                         begin=i;
      |                         ^~~~~
/usr/include/c++/14/valarray:1238:5: note: candidates are: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227:5: note:                 'template<class _Tp> _Tp* std::begin(valarray<_Tp>&)'
 1227 |     begin(valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note:                 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
   95 |     begin(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&)'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:52:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&)'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/initializer_list:88:5: note:                 'template<class _Tp> constexpr const _Tp* std::begin(initializer_list<_Tp>)'
   88 |     begin(initializer_list<_Tp> __ils) noexcept
      |     ^~~~~
a.cc:79:7: note:                 'int begin'
   79 | int n,begin,ans;
      |       ^~~~~
a.cc:128:42: error: reference to 'begin' is ambiguous
  128 |                         v[i+1].push_back(begin);
      |                                          ^~~~~
/usr/include/c++/14/valarray:1238:5: note: candidates are: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227:5: note:                 'template<class _Tp> _Tp* std::begin(valarray<_Tp>&)'
 1227 |     begin(valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note:                 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
   95 |     begin(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&)'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:52:5: note:                 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&)'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/initializer_list:88:5: note:                 'template<class _Tp> constexpr const _Tp* std::begin(initializer_list<_Tp>)'
   88 |     begin(initializer_list<_Tp> __ils) noexcept
      |     ^~~~~
a.cc:79:7: note:                 'int begin'
   79 | int n,begin,ans;
      |       ^~~~~
a.cc:130:42: error: reference to 'begin' is ambiguous
  130 |                         v[i+2].push_back(begin);
      |                                          ^~~~~
/usr/include/c++/14/valarray:1238:5: note: candidates are: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227: