HDU 1255

题目大意：求矩形相交部分面积和

#include<iostream>#include<algorithm>using namespace std;#define N 2001struct node{    int l,r,cover;    double one_len,more_len;    int getmid(){        return (l+r)>>1;    }}p[3*N];struct Line{    double l,r,h;    int flag;}L[N];int m;double X[N];double h[N];bool cmp(Line x,Line y){    return x.h<y.h;}int find(double x){    int f=0,l=m-1;    while(f<=l)    {        int mid=(f+l)>>1;        if(h[mid]==x)            return mid;        if(h[mid]>x)            l=mid-1;        else            f=mid+1;    }}void setlen(int id){    int l=p[id].l,r=p[id].r;    if(p[id].cover>1)        p[id].one_len=p[id].more_len=h[r]-h[l];    else if(p[id].cover==1)    {        p[id].one_len=h[r]-h[l];        if(p[id].l+1==p[id].r)            p[id].more_len=0;        else            p[id].more_len=p[id<<1].one_len+p[id<<1|1].one_len;    }    else    {        if(p[id].l+1==p[id].r)            p[id].more_len=p[id].one_len=0;        else        {            p[id].more_len=p[id<<1].more_len+p[id<<1|1].more_len;            p[id].one_len=p[id<<1].one_len+p[id<<1|1].one_len;        }    }}void build(int l,int r,int id){    p[id].l=l;    p[id].r=r;    p[id].cover=0;    p[id].one_len=p[id].more_len=0;    if(r-l==1)        return;    int mid=p[id].getmid();    build(l,mid,id<<1);    build(mid,r,id<<1|1);}void update(int l,int r,int flag,int id){    if(p[id].l==l&&r==p[id].r)    {        p[id].cover+=flag;        setlen(id);        return;    }    int mid=p[id].getmid();    if(r<=mid)        update(l,r,flag,id<<1);    else if(l>=mid)        update(l,r,flag,id<<1|1);    else    {        update(l,mid,flag,id<<1);        update(mid,r,flag,id<<1|1);    }    setlen(id);}int main(void){    int t;    scanf("%d",&t);    while(t--)    {        int n;        scanf("%d",&n);        m=0;        while(n--)        {            double x1,y1,x2,y2;            scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);            X[m]=x1;            L[m].l=x1;            L[m].r=x2;            L[m].h=y1;            L[m].flag=1;            m++;            X[m]=x2;            L[m].l=x1;            L[m].r=x2;            L[m].h=y2;            L[m].flag=-1;            m++;        }        sort(X,X+m);        sort(L,L+m,cmp);        build(0,m-1,1);        int mm=m;        m=1;        h[0]=X[0];        for(int i=1;i<mm;i++)            if(X[i]!=X[i-1])                h[m++]=X[i];        double ans=0;        for(int i=0;i<mm-1;i++)        {            int l=find(L[i].l);            int r=find(L[i].r);            update(l,r,L[i].flag,1);            ans+=p[1].more_len*(L[i+1].h-L[i].h);        }        printf("%.2lf/n",ans);    }} 

此时线段区间的变量不能是单纯一个len了，如果只用一个变量len的话，每次update的时候就要更新到底，这样浪费很多时间，可以设置两个变量：one_len, more_len。分别记录此区间覆盖次数>=1与>=2的长度，最后用的结果就是more_len,函数setlen()描述了如何更新这两个变量