HDU 4007 Dave (11-year Dalian line segment tree + discretization + scanning line)

Reprint please indicate the source, thank you http://blog.csdn.net/ACM_cxlove? Viewmode = Contents
By --- cxlove

Question: give some points, give a square with a link length of R, and ask how many points can be covered

Http://acm.hdu.edu.cn/showproblem.php? PID = 1, 4007

In my memory, this question was quite difficult at the time and I was not clear about the question.

The side of a square is parallel to the coordinate axis, so there is more water. The scope is not very large.

For each vertex, take him as the lower left corner to create a square, and then calculate a rectangle intersection for all the squares to find the most covered number.

Actually not very familiar with scanning lines, refer. It is convenient to create a label for the upper and lower sides.

#include<iostream>#include<cstdio>#include<map>#include<cstring>#include<cmath>#include<vector>#include<queue>#include<algorithm>#include<set>#define inf 110000#define N 1005#define Min(a,b) ((a)<(b)?(a):(b))#define Max(a,b) ((a)>(b)?(a):(b))#define pb(a) push_back(a)#define mem(a,b) memset(a,b,sizeof(a))#define eps 1e-9#define zero(a) fabs(a)<eps#define LL long long#define lson (step<<1)#define rson (step<<1|1)#define MOD 1000000007using namespace std;struct Node{int left,right,mid,cover,val;}L[N*2*4];struct Seg{int y,x1,x2;int flag;Seg(){}Seg(int _y,int _x1,int _x2,int _flag):y(_y),x1(_x1),x2(_x2),flag(_flag){}bool operator<(const Seg s)const{return s.y==y?s.flag<flag:s.y>y;}}seg[N*2];int n,r,x[N*2],m;int BinSearch(int num){int low=0,high=m-1,mid;while(low<=high){mid=(low+high)/2;if(x[mid]==num) return mid;if(x[mid]<num) low=mid+1;else high=mid-1;}}void Bulid(int step,int l,int r){L[step].left=l;L[step].right=r;L[step].mid=(l+r)/2;L[step].cover=L[step].val=0;if(l==r) return;Bulid(lson,l,L[step].mid);Bulid(rson,L[step].mid+1,r);}void Push_Down(int step){if(L[step].cover){L[lson].cover+=L[step].cover;L[rson].cover+=L[step].cover;L[lson].val+=L[step].cover;L[rson].val+=L[step].cover;L[step].cover=0;}}void Push_Up(int step){L[step].val=max(L[lson].val,L[rson].val);}void Update(int step,int l,int r,int c){if(L[step].left==l&&L[step].right==r){L[step].cover+=c;L[step].val+=c;return;}Push_Down(step);if(r<=L[step].mid) Update(lson,l,r,c);else if(l>L[step].mid) Update(rson,l,r,c);else{Update(lson,l,L[step].mid,c);Update(rson,L[step].mid+1,r,c);}Push_Up(step);}int main(){while(scanf("%d%d",&n,&r)!=EOF){for(int i=0;i<n;i++){int X,Y;scanf("%d%d",&X,&Y);x[i*2]=X;x[i*2+1]=X+r+1;seg[i*2]=Seg(Y,X,X+r+1,1);seg[i*2+1]=Seg(Y+r+1,X,X+r+1,-1);}sort(x,x+2*n);sort(seg,seg+2*n);m=1;for(int i=1;i<2*n;i++)if(x[i]!=x[m-1])x[m++]=x[i];Bulid(1,0,m-1);int ans=0;for(int i=0;i<2*n;i++){int left=BinSearch(seg[i].x1),right=BinSearch(seg[i].x2);Update(1,left,right,seg[i].flag);if(L[1].val>ans) ans=L[1].val;}printf("%d\n",ans);}return 0;}