BZOJ_1654_[Usaco2007 Open]City Horizon 城市地平线_扫描线

Description

N个矩形块,交求面积并.

Input

* Line 1: A single integer: N

* Lines 2..N+1: Input line i+1 describes building i with three space-separated integers: A_i, B_i, and H_i

Output

* Line 1: The total area, in square units, of the silhouettes formed by all N buildings

Sample Input

4
2 5 1
9 10 4
6 8 2
4 6 3

Sample Output

16



裸的扫描线,这里从左往右扫。

先将x轴向上平移一个单位,避免处理麻烦的区间长度问题。

然后每个矩形拆成两条竖线,从左往右扫。

需要在线段树上维护一些点是否存在。

每个节点记录sum和raw,当sum>0时raw=r-l+1,否则等于两个儿子的raw之和,每次修改都要pushup一下。

代码:

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define N 80050
#define maxn 1000000000
struct Line {
    int y_1,y_2,x,flg;
    Line() {}
    Line(int y__1,int y__2,int x_,int flg_) :
        y_1(y__1),y_2(y__2),x(x_),flg(flg_) {}
    bool operator < (const Line &u) const {
        return x<u.x;
    }
}a[N];
int t[N*40],ls[N*40],rs[N*40],cnt,n,raw[N*40],add[N*40];
void pushdown(int l,int r,int &p,int v) {
    if(!p) p=++cnt;
    t[p]+=(r-l+1)*v; add[p]+=v;
}
void pushup(int l,int r,int p) {
    if(t[p]>0) raw[p]=r-l+1;
    else if(l==r) raw[p]=0;
    else raw[p]=raw[ls[p]]+raw[rs[p]];
}
void update(int l,int r,int x,int y,int v,int &p) {
    if(!p) p=++cnt;
    if(x<=l&&y>=r) {
        t[p]+=v; pushup(l,r,p);
        return ;
    }
    int mid=(l+r)>>1;
    if(add[p]) {
        pushdown(l,mid,ls[p],add[p]); pushdown(mid+1,r,rs[p],add[p]); add[p]=0;
    }
    if(x<=mid) update(l,mid,x,y,v,ls[p]);
    if(y>mid) update(mid+1,r,x,y,v,rs[p]);
    pushup(l,r,p);
}
int main() {
    scanf("%d",&n);
    int i,x_1,x_2,h,tot=0;
    for(i=1;i<=n;i++) {
        scanf("%d%d%d",&x_1,&x_2,&h);
        a[++tot]=Line(1,h,x_1,1);
        a[++tot]=Line(1,h,x_2,-1);
    }
    sort(a+1,a+tot+1);
    int root=0;
    update(1,maxn,a[1].y_1,a[1].y_2,a[1].flg,root);
    long long ans=0;
    for(i=2;i<=tot;i++) {
        ans+=1ll*(a[i].x-a[i-1].x)*raw[1];
        update(1,maxn,a[i].y_1,a[i].y_2,a[i].flg,root);
    }
    printf("%lld\n",ans);
}

原文地址:https://www.cnblogs.com/suika/p/9063254.html

时间: 2024-11-13 09:40:50

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