Atlantis HDU - 1542 （扫描线 + 线段树）

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https://cn.vjudge.net/problem/HDU-1542

题意

求矩形覆盖的面积

思路

模板题

#include <bits/stdc++.h>

using namespace std;
const int maxn = 210;
int n,cnt,num,p;
double ls[maxn*2],ans;
struct edg  ///边
{
    double l,r,h;
    int flag; ///1为下线 -1为上线
    bool operator < (const edg &b)const{
        return h < b.h;
    }
}edge[maxn];
struct node ///线段树
{
    int l,r,lazy;
    double len;
}tree[maxn*4];

void add(double x1,double x2,double h,int f)
{
    edge[cnt].l = x1;
    edge[cnt].r = x2;
    edge[cnt].h = h;
    edge[cnt++].flag = f;
}

void build(int rt,int l,int r)
{
    tree[rt].l = l;
    tree[rt].r = r;
    tree[rt].len = 0;
    tree[rt].lazy = 0;
    if(l == r) return ;
    int mid = (l+r)>>1;
    build(rt<<1,l,mid);
    build(rt<<1|1,mid+1,r);
}
void pushup(int rt)
{
    if(tree[rt].lazy) /// 存在
    {
        tree[rt].len = ls[tree[rt].r+1] - ls[tree[rt].l];
    }
    else if(tree[rt].l == tree[rt].r) ///最小距离 为0
    {
        tree[rt].len = 0;
    }
    else tree[rt].len = tree[rt<<1].len + tree[rt<<1|1].len; ///不存在整段 但可能存在部分
}
void updata(int rt,int l,int r,int val)
{
    if(tree[rt].l == l&&tree[rt].r == r)
    {
        tree[rt].lazy += val;///新增或者去掉
        pushup(rt);
        return ;
    }
    int mid = (tree[rt].l + tree[rt].r)>>1;
    if(l > mid)
        updata(rt<<1|1,l,r,val);
    else if(mid >= r)
        updata(rt<<1,l,r,val);
    else
    {
        updata(rt<<1,l,mid,val);
        updata(rt<<1|1,mid+1,r,val);
    }
    pushup(rt);

}
int main()
{
    int i,j,k;
    int ca = 1;
    while(scanf("%d",&n) != EOF&&n)
    {
        ans = cnt = p = 0;
        for(i=1;i<=n;i++)
        {
            double x1,x2,y1,y2;
            scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
            add(x1,x2,y1,1);
            add(x1,x2,y2,-1);
            ls[p++] = x1;
            ls[p++] = x2;
        }
        sort(edge,edge+cnt); ///从下向上扫描
        sort(ls,ls+p);
        int m = unique(ls,ls+p) - ls; ///去重 m为驱虫后元素个数
        build(1,0,m-1);
        for(i=0;i<cnt-1;i++)
        {
            int l = lower_bound(ls,ls+m,edge[i].l) - ls; ///找到对应的位置
            int r = lower_bound(ls,ls+m,edge[i].r) - ls;
            updata(1,l,r-1,edge[i].flag); ///修改
            ans += (edge[i+1].h - edge[i].h) * tree[1].len;///只有有高度差才会改变
        }
        printf("Test case #%d\n",ca++);
        printf("Total explored area: %.2f\n\n",ans);
    }
    return 0;
}