Submission #73871

#	Time	Username	Problem	Language	Result	Execution time	Memory
73871		zscoder	Election (BOI18_election)	C++17	82 / 100	1665 ms	263168 KiB

election

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
using namespace std;
using namespace __gnu_pbds;
 
#define fi first
#define se second
#define mp make_pair
#define pb push_back
 
typedef long long ll;
typedef pair<int,int> ii;
typedef vector<int> vi;
typedef long double ld; 
typedef tree<ii, null_type, less<ii>, rb_tree_tag, tree_order_statistics_node_update> pbds;
 
char s[555555];
int n;
int del[555555];
 
int solve_naive(int l, int r)
{
	int cnt=0;
	for(int i=l;i<=r;i++) del[i]=0;
	int ans=0; int S=0; int minpref=0;
	for(int i=l;i<=r;i++)
	{
		S+=(s[i]=='C'?1:-1);
		if(s[i]=='C') cnt++;
		else cnt--;
		if(cnt<0)
		{
			del[i]=1; ans++;
			cnt++;
		}
	}
	minpref=-ans;
	int positive = S - minpref;
	cnt=0; int mx=0;
	for(int i=r;i>=l;i--)
	{
		if(del[i]) 
		{
			cnt = positive; continue;
		}
		if(s[i]=='C') cnt++;
		else cnt--;
		if(cnt<0)
		{
			mx=max(mx,abs(cnt));	
		}
	}
	return ans+mx;
}
 
 
struct node
{
	int sum;
	vi vec;
	vi sufmax;
	int minprefback;
	vi prefmax;
	int lastneg;
};
 
node st[511111*4];
 
void outnode(node S)
{
	cout<<"SUM : "<<S.sum<<'\n';
	for(int v:S.vec)
	{
		cout<<v<<' ';
	}
	cout<<'\n';
	cout<<"MIN PREF FROM BACK : "<<S.minprefback<<'\n';
	cout<<"LAST NEGATIVE : "<<S.lastneg<<'\n';
}
 
node compute(int l, int r)
{
	node N;
	N.sum=0;
	for(int i=l;i<=r;i++) del[i]=0;
	int cnt=0; int minpref=0;
	for(int i=l;i<=r;i++)
	{
		N.sum+=(s[i]=='C'?1:-1);
		cnt+=(s[i]=='C'?1:-1);
		if(cnt<0)
		{
			del[i]=1; cnt++; minpref--;
		}
	}
	N.minprefback=0; cnt=0;
	for(int i=r;i>=l;i--)
	{
		cnt+=(s[i]=='C'?1:-1);
		N.minprefback=min(N.minprefback, cnt);
	}
	N.minprefback*=-1;
	cnt=0; int mn = 0; bool ex=0; N.lastneg=0;
	for(int i=r;i>=l;i--)
	{
		if(del[i])
		{
			if(!ex)
			{
				N.lastneg=abs(mn);
			}
			else
			{
				N.vec.pb(abs(mn));
			}
			cnt=0; mn=0;
			ex=1;
		}
		else
		{
			cnt+=(s[i]=='C'?1:-1);
			mn = min(mn, cnt);
		}
	}
	if(!ex)
	{
		N.lastneg = abs(mn);
	}
	else
	{
		N.vec.pb(abs(mn));
	}
	reverse(N.vec.begin(),N.vec.end());
	N.sufmax.resize(int(N.vec.size()));
	for(int i=int(N.vec.size())-1;i>=0;i--)
	{
		N.sufmax[i] = N.vec[i];
		if(i+1<N.vec.size()) N.sufmax[i]=max(N.sufmax[i+1], N.sufmax[i]);
	}
	N.prefmax.resize(int(N.vec.size()));
	for(int i=0;i<N.vec.size();i++)
	{
		N.prefmax[i] = N.vec[i]-i;
		if(i>0) N.prefmax[i]=max(N.prefmax[i-1],N.prefmax[i]);
	}
	return N;
}
 
void build(int id, int l, int r)
{
	st[id] = compute(l,r-1);
	if(r-l<2) return ;
	int mid=(l+r)>>1;
	build(id*2,l,mid); build(id*2+1,mid,r);
}

vi nodes;
 
void query(int id, int l, int r, int ql, int qr) //get which nodes i need to care for my query
{
	if(ql>=r||l>=qr) return ;
	if(ql<=l&&r<=qr) 
	{
		nodes.pb(id);
		//cerr<<"NODE : "<<l<<' '<<r-1<<'\n';
		return ;
	}
	int mid=(l+r)>>1;
	query(id*2,l,mid,ql,qr);
	query(id*2+1,mid,r,ql,qr);
}
const int DEBUG = 0;
int main()
{
	//ios_base::sync_with_stdio(0); cin.tie(0);
	if(!DEBUG)
	{
		scanf("%d",&n); scanf("%s",s);
	}
	if(DEBUG)
	{
		srand(time(NULL));
		freopen("election_boi.in","w",stdout);
		n=100; 
		for(int i=0;i<n;i++) s[i] = (rand()&1?'C':'T');
	}
	if(DEBUG) cout<<n<<'\n'<<s<<'\n';
	int q; 
	if(!DEBUG) cin>>q;
	if(DEBUG) 
	{
		q=500;
		cout<<q<<'\n';
	}
	build(1,0,n);
	//outnode(st[1]);
	for(int i=0;i<q;i++)
	{
		int l,r; 
		if(!DEBUG)
		{
			//cin>>l>>r;
			scanf("%d %d",&l,&r); 
			l--; r--;
		}
		if(DEBUG)
		{
			l=rand()%n; r=rand()%n;
			if(l>r) swap(l,r);
			cout<<l+1<<' '<<r+1<<'\n';
		}
		nodes.clear();
		query(1,0,n,l,r+1);
		int Lcnt = 0; 
		int Rcnt = 0;
		int maxmiddle = 0;
		int curL = 0; int minpref = 0;
		for(int v:nodes)
		{
			//curL of the vec elements will be rekted
			int badbrackets = st[v].vec.size();
			if(badbrackets==0)
			{
				minpref = max(st[v].lastneg, minpref - st[v].sum);
				curL += st[v].sum;
			}
			else
			{
				if(curL>=badbrackets)
				{
					minpref = max(st[v].minprefback, minpref - st[v].sum);
					curL-=badbrackets;
					curL+=st[v].sum+badbrackets;
				}
				else
				{
					maxmiddle = max(maxmiddle, st[v].prefmax[curL] + curL);
					maxmiddle = max(maxmiddle, minpref + curL);
					Lcnt += badbrackets - curL;
					if(curL+1<st[v].sufmax.size()) maxmiddle = max(maxmiddle, st[v].sufmax[curL+1]);
					curL = st[v].sum + badbrackets;
					minpref = st[v].lastneg;
				}
			}
			/*
			outnode(st[v]);
			cerr<<"MINPREF : "<<minpref<<'\n';
			cerr<<"CURL : "<<curL<<'\n';
			cerr<<"LCNT : "<<Lcnt<<'\n';
			cerr<<'\n';
			*/
		}
		Rcnt = max(Rcnt, max(minpref, maxmiddle - curL));
		int ans=Lcnt+Rcnt;
		if(DEBUG)
		{
			if(ans!=solve_naive(l,r))
			{
				assert(0);
				cerr<<"HERE"<<'\n';
			}
			cerr<<ans<<' '<<solve_naive(l,r)<<'\n';
		}
		else
		{
			//cout<<ans<<' '<<solve_naive(l,r)<<'\n';
			printf("%d\n",ans);
		}
		//cout<<solve(l,r)<<'\n';
	}
}

Compilation message (stderr)

election.cpp: In function 'node compute(int, int)':
election.cpp:140:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(i+1<N.vec.size()) N.sufmax[i]=max(N.sufmax[i+1], N.sufmax[i]);
      ~~~^~~~~~~~~~~~~
election.cpp:143:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<N.vec.size();i++)
              ~^~~~~~~~~~~~~
election.cpp: In function 'int main()':
election.cpp:242:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
      if(curL+1<st[v].sufmax.size()) maxmiddle = max(maxmiddle, st[v].sufmax[curL+1]);
         ~~~~~~^~~~~~~~~~~~~~~~~~~~
election.cpp:180:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&n); scanf("%s",s);
   ~~~~~^~~~~~~~~
election.cpp:180:24: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&n); scanf("%s",s);
                   ~~~~~^~~~~~~~
election.cpp:185:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   freopen("election_boi.in","w",stdout);
   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
election.cpp:205:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%d %d",&l,&r); 
    ~~~~~^~~~~~~~~~~~~~~

• Subtask 1: 28 / 28
• Subtask 2: 54 / 54
• Subtask 3: 0 / 18