BZOJ4049 : [Cerc2014] Mountainous landscape

Claris發表於2015-08-04

對於區間[l,r],若詢問的直線與該區間的凸殼有交,則有解。

線上段樹每個區間上維護凸殼,然後查詢時在相應凸殼上二分斜率即可,時間複雜度$O(n\log^2n)$。

 

#include<cstdio>
#define N 262145
typedef long long ll;
int T,n,i,c,l[N],r[N],t;
struct P{
  int x,y;
  P(){}
  P(int _x,int _y){x=_x,y=_y;}
  inline P operator-(P b){return P(x-b.x,y-b.y);}
  inline ll operator*(P b){return(ll)x*b.y-(ll)y*b.x;}
}p[100010],A,B,q[1900000];
void build(int x,int a,int b){
  q[l[x]=++t]=p[a];
  for(int i=a+1;i<=b+1;q[++t]=p[i++])while(t>l[x]&&(p[i]-q[t])*(q[t]-q[t-1])<=0)t--;
  r[x]=t;
  if(a==b)return;
  int mid=(a+b)>>1;
  build(x<<1,a,mid),build(x<<1|1,mid+1,b);
}
inline bool ex(int l,int r){
  int mid,t=l++;
  while(l<=r){
    mid=(l+r)>>1;
    if((q[mid]-A)*(B-q[mid])<(q[mid-1]-A)*(B-q[mid-1]))l=(t=mid)+1;else r=mid-1;
  }
  return(q[t]-A)*(B-q[t])<0;
}
int ask(int x,int a,int b){
  if(c<=a){
    if(!ex(l[x],r[x]))return 0;
    if(a==b)return a;
  }
  int mid=(a+b)>>1;
  if(c<=mid){
    int t=ask(x<<1,a,mid);
    if(t)return t;
  }
  return ask(x<<1|1,mid+1,b);
}
inline void read(int&a){char c;while(!(((c=getchar())>='0')&&(c<='9')));a=c-'0';while(((c=getchar())>='0')&&(c<='9'))(a*=10)+=c-'0';}
int main(){
  for(read(T);T--;puts("0")){
    for(read(n),i=1;i<=n;i++)read(p[i].x),read(p[i].y);
    for(t=0,build(1,1,n-1),i=1;i<n-1;i++)A=p[i],B=p[i+1],c=i+1,printf("%d ",ask(1,1,n-1));
  }
  return 0;
}