# HDU 5091 Beam Cannon

Source: Internet
Author: User

Main topic:

There are n points (n<=10000), the coordinates of the point are not more than 20000, and then ask you to use a w*h (1<=w,h<=40000) Rectangle, the edge of the rectangle parallel to the axis, the maximum number of points can be covered.

Rujia Black Book has the original problem

The code below is discretized, scanned with a straight line perpendicular to the x axis, and a line tree on the y axis, so for each point (x, y), give the weight of 1, and then add a new negative point (x+w,y), giving the weight-1. When the scan line sweeps through each point, the segment tree is updated with the weighted value of the point. Maintain the sum value for each interval, because it is an interval update, so you have to make a lazy tag.

`1#include <stdio.h>2#include <stdlib.h>3#include <math.h>4#include <string.h>5#include <iostream>6#include <string>7#include <map>8#include <Set>9#include <algorithm>Ten#include <queue> One#include <vector> A #defineN 40000 - using namespacestd; -  the structNode - { -     intL,r,lazy; -     intsum; +} node[n<<2]; - struct Line + { A     intx,y1,y2,v; at Line () {} -Line (intAintBintCintd) -     { -x=a,y1=b,y2=c,v=D; -     } -     BOOL operator< (ConstLine&a)Const in     { -         if(x==a.x) to             returnV>A.V; +         returnx<a.x; -     } the } Line[n]; * intLisan[n]; \$ intCnt=0;Panax Notoginseng voidPushup (intRT) - { theNode[rt].sum=max (node[rt<<1].sum,node[rt<<1|1].sum); + } A voidPushdown (intRT) the { +     if(Node[rt].lazy) -     { \$node[rt<<1].lazy+=Node[rt].lazy; \$node[rt<<1|1].lazy+=Node[rt].lazy; -node[rt<<1].sum+=Node[rt].lazy; -node[rt<<1|1].sum+=Node[rt].lazy; thenode[rt].lazy=0; -     }Wuyi } the voidBuildintRtintLintR) - { Wunode[rt].sum=0, node[rt].lazy=0; -Node[rt].l=l,node[rt].r=R; About     if(l==R) \$         return; -     intMid=l+r>>1; -Build (rt<<1, l,mid); -Build (rt<<1|1, mid+1, R); A pushup (RT); + } the voidUpdateintRtintLintRintv) - { \$     if(l<=node[rt].l&&node[rt].r<=R) the     { thenode[rt].lazy+=v; thenode[rt].sum+=v; the         return; -     } in pushdown (RT); the     intMid=node[rt].l+node[rt].r>>1; the     if(l<=mid) AboutUpdate (rt<<1, l,r,v); the     if(r>mid) theUpdate (rt<<1|1, l,r,v); the pushup (RT); + } - intQueryintRtintLintR) the {Bayi     if(l<=node[rt].l&&node[rt].r<=R) the     { the         returnnode[rt].sum; -     } - pushdown (RT); the     intMid=node[rt].l+node[rt].r>>1, ans=0; the     if(l<=mid) theAns+=query (rt<<1, l,r); the     if(r>mid) -Ans+=query (rt<<1|1, l,r); the     returnans; the } the intMain ()94 { the     intn,w,h; the      while(SCANF ("%d",&N)) the     {98Cnt=0; About         if(n<0) -              Break;101scanf"%d%d",&w,&h);102          for(intI=0; i<n;++i)103         {104             intx, y; thescanf"%d%d",&x,&y);106x+=20001;107y+=20001;108lisan[cnt]=y;109Line[cnt++]=line (X,y,y+h,1); thelisan[cnt]=y+h;111Line[cnt++]=line (x+w,y,y+h,-1); the         }113Sort (line,line+CNT); theSort (lisan,lisan+CNT); the         intNum=unique (LISAN,LISAN+CNT)-Lisan; theBuild1,0, num-1);117         intans=0;118          for(intI=0; i<cnt;++i)119         { -             intL=lower_bound (LISAN,LISAN+NUM,LINE[I].Y1)-Lisan;121             intR=lower_bound (Lisan,lisan+num,line[i].y2)-Lisan;122Update1, L,R,LINE[I].V);123Ans=max (ans,node[1].sum);124         } theprintf"%d\n", ans);126     }127  -}`

HDU 5091 Beam Cannon

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