【线段树+扫描线】 HDOJ 1255 覆盖的面积

来源：互联网发布：淘宝产品图片拍摄技巧编辑：程序博客网时间：2024/06/05 05:41

线段树+扫描线+离散化，算是比较经典的题目吧，我自己做的时候不会做，百度的题解。。。发现不需要用pushdown，只用pushup就可以解决。。。pushup的代码如下

void pushup(int o, int L, int R){if(cover[o]==0){once[o]=once[o<<1]+once[o<<1 | 1];more[o]=more[o<<1]+more[o<<1 | 1];}if(cover[o]==1){once[o]=x[R+1]-x[L];more[o]=once[o<<1]+once[o<<1 | 1];}if(cover[o]==2)once[o]=more[o]=x[R+1]-x[L];}

其中once代表覆盖一次及以上的面积，more代表覆盖两次及以上的面积，cover是覆盖的次数，同时也是lazy标记。

其他的部分都不难。。。

#include <iostream>#include <sstream>#include <algorithm>#include <vector>#include <queue>#include <stack>#include <map>#include <set>#include <bitset>#include <cstdio>#include <cstring>#include <cstdlib>#include <cmath>#include <climits>#define maxn 10005#define eps 1e-6#define mod 200000007#define INF 99999999#define lowbit(x) (x&(-x))#define lson o<<1, L, mid#define rson o<<1 | 1, mid+1, Rtypedef long long LL;using namespace std;double x[maxn];double once[maxn];double more[maxn];int cover[maxn];int xcnt;struct segment{double x1, x2, h;int flag;}seg[maxn];int ql, qr, k;int n, m;double ans;int cmp1(double a, double b){return a<b;}int cmp2(segment a, segment b){return a.h<b.h;}int search(double tmp){int bot=1, top=xcnt, mid;while(top>=bot){mid=(bot+top)>>1;if(abs(x[mid]-tmp)<eps) break;if(x[mid]>tmp) top=mid-1;else bot=mid+1;}return mid;}void read(void){int i, j;scanf("%d",&n);xcnt=1;for(i=0, j=0;i<n;i++){scanf("%lf%lf", &seg[j].x1, &seg[j].h);scanf("%lf%lf", &seg[j+1].x2, &seg[j+1].h);seg[j].flag=1, seg[j+1].flag=-1;seg[j].x2=seg[j+1].x2, seg[j+1].x1=seg[j].x1;x[xcnt++]=seg[j].x1, x[xcnt++]=seg[j].x2, j+=2;}xcnt--, m=j;sort(x+1, x+xcnt+1, cmp1);for(i=2, j=2;i<=xcnt;i++)if(abs(x[i]-x[i-1])>eps)x[j++]=x[i];xcnt=j-1;sort(seg, seg+m, cmp2);}void init(void){memset(once, 0, sizeof once);memset(more, 0, sizeof more);memset(cover, 0, sizeof cover);}void pushup(int o, int L, int R){if(cover[o]==0){once[o]=once[o<<1]+once[o<<1 | 1];more[o]=more[o<<1]+more[o<<1 | 1];}if(cover[o]==1){once[o]=x[R+1]-x[L];more[o]=once[o<<1]+once[o<<1 | 1];}if(cover[o]==2)once[o]=more[o]=x[R+1]-x[L];}void updata(int o, int L, int R){if(ql<=L && qr>=R){cover[o]+=k;pushup(o, L, R);return;}int mid=(R+L)>>1;if(ql<=mid) updata(lson);if(qr>mid) updata(rson);pushup(o, L, R);}void work(void){double tmp=0;double res=0;ql=search(seg[0].x1), qr=search(seg[0].x2)-1;k=seg[0].flag;updata(1, 1, xcnt-1);for(int i=1;i<m;i++){ql=search(seg[i].x1), qr=search(seg[i].x2)-1;k=seg[i].flag;res+=more[1]*(seg[i].h-tmp);tmp=seg[i].h;updata(1, 1, xcnt-1);}printf("%.2f\n", res);}int main(void){int _;while(scanf("%d",&_)!=EOF){while(_--){init();read();work();}}return 0;}

0 0