Submission #130935

#	Time	Username	Problem	Language	Result	Execution time	Memory
130935		fefe	Aliens (IOI16_aliens)	C++17	100 / 100	113 ms	8696 KiB

aliens

#include<bits/stdc++.h>
#include "aliens.h"
#define MAX_N 100005
#define sq(x) ((x)*(x))
#define inf (1LL<<60)
using namespace std;
typedef long long LL;
typedef pair<LL,LL> pil;
struct node{
	LL s,e;
}V[MAX_N];
struct line{
	LL a,b,c;
}L[MAX_N];
LL n,k,ans;
LL dp[MAX_N],from[MAX_N];
bool is_ok(line a,line b,line c){
	return (b.b-a.b)*(b.a-c.a)<(a.a-b.a)*(c.b-b.b);
}
LL CHT(LL c){
	LL s,e;
	LL i;
	s=e=0;
	L[e++]={-2*V[1].s,sq(V[1].s)-2*V[1].s,0};
	for(i=1;i<=n;i++){
		while(e-s>1 && L[s].a*V[i].e+L[s].b>=L[s+1].a*V[i].e+L[s+1].b)	s++;
		dp[i]=L[s].a*V[i].e+L[s].b+sq(V[i].e+1)+c;
		from[i]=L[s].c;
		line p={-2*V[i+1].s,sq(V[i+1].s)-2*V[i+1].s+dp[i]};
		if(V[i].e-V[i+1].s+1>0)	p.b-=sq(V[i].e-V[i+1].s+1);
		p.c=i;
		while(e-s>1 && !is_ok(L[e-2],L[e-1],p))	e--;
		L[e++]=p;
	}
	for(c=0,i=n;i;i=from[i],c++);
	return c;
}
long long take_photos(int N, int m, int K, std::vector<int> r, std::vector<int> c) {	
	LL i,s=0,e=(long long)m*m;
	n=N;
	k=K;
	for(i=1;i<=n;i++){
		V[i].s=min(r[i-1],c[i-1]);
		V[i].e=max(r[i-1],c[i-1]);
	}
	sort(V+1,V+n+1,[&](const node x,const node y){return (x.s==y.s)?(x.e>y.e):(x.s<y.s);});
	
	m=0;
	LL x=-10000;
	for(i=1;i<=n;i++){
		if(x<V[i].e)	V[++m]=V[i];
		x=max(x,V[i].e);
	}
	
	n=m;
	sort(V+1,V+n+1,[&](const node x,const node y){return x.e<y.e;});
	ans=inf;
	k=min(n,k);
	bool Z=false;
	LL lx=inf,lv,rx=-inf,rv;
	while(s<=e){
		LL mid=(s+e)>>1;
		x=CHT(mid);
		if(x==k){
			return dp[n]-mid*x;
		}else if(x<k){
			rx=x;rv=dp[n]-mid*x;
			e=mid-1;
		}else{
			lx=x;lv=dp[n]-mid*x;
			s=mid+1;
		}
	}
		
	return rv+(lv-rv)/(rx-lx)*(rx-k);
}

Compilation message (stderr)

aliens.cpp: In function 'long long int take_photos(int, int, int, std::vector<int>, std::vector<int>)':
aliens.cpp:59:7: warning: unused variable 'Z' [-Wunused-variable]
  bool Z=false;
       ^
aliens.cpp:75:33: warning: 'rv' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return rv+(lv-rv)/(rx-lx)*(rx-k);
                                 ^
aliens.cpp:75:15: warning: 'lv' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return rv+(lv-rv)/(rx-lx)*(rx-k);
            ~~~^~~~

• Subtask 1: 4 / 4
• Subtask 2: 12 / 12
• Subtask 3: 9 / 9
• Subtask 4: 16 / 16
• Subtask 5: 19 / 19
• Subtask 6: 40 / 40