POJ 1151 Atlantis（线段树-扫描线，矩形面积并）

题目链接：http://poj.org/problem?id=1151

题目大意：坐标轴上给你n个矩形， 问这n个矩形覆盖的面积

题目思路：矩形面积并。

代码如下：

#include<stdio.h>
#include<vector>
#include<algorithm>
using namespace std;
const int N = ;
struct Line
{
    int l, r, flag;
    double h;
    Line(){}
    Line(int l, int r, int flag, double h):l(l), r(r), flag(flag), h(h) {}
    bool operator<(Line &b) const
    {
        return h<b.h;
    }
};

int n;
vector<double> vec;
vector<Line>line;

struct node
{
    int l, r, flag;
    double len;
};
node tree[N << ];

void build(int l, int r, int k)
{
    tree[k].l = l, tree[k].r = r, tree[k].len = , tree[k].flag = ;
    if(l == r - )
        return;
    int mid = (l + r) >> ;
    build(l, mid, k<<);
    build(mid, r, k<<|);
}

void updata_up(int k)
{
    if(tree[k].flag)
        tree[k].len = vec[tree[k].r-] - vec[tree[k].l-];
    else if (tree[k].l == tree[k].r - )
        tree[k].len = ;
    else
        tree[k].len = tree[k<<].len + tree[k<<|].len;
}

void updata(int l, int r, int k, int x)
{
    if(tree[k].l >= l && tree[k].r <= r)
    {
        tree[k].flag += x;
        updata_up(k);
        return;
    }

    if(tree[k<<].r > l)
        updata(l, r, k<<, x);
    if(tree[k<<|].l < r)
        updata(l, r, k<<|, x);

    updata_up(k);
}

int main()
{
    int cases = ;
    while(scanf("%d", &n),n)
    {
        vec.clear();
        line.clear();
        double x1[], y1[], x2[], y2[];
        for(int i=; i<n; ++ i)
        {
            scanf("%lf%lf%lf%lf", &x1[i], &y1[i], &x2[i], &y2[i]);
            vec.push_back(x1[i]);
            vec.push_back(x2[i]);
        }
        sort(vec.begin(), vec.end());
        vec.erase(unique(vec.begin(), vec.end()), vec.end());
        for(int i=; i<n; ++ i)
        {
            int x = lower_bound(vec.begin(), vec.end(), x1[i]) - vec.begin() + ;
            int y = lower_bound(vec.begin(), vec.end(), x2[i]) - vec.begin() + ;

            line.push_back(Line(x, y, , y1[i]));
            line.push_back(Line(x, y, -, y2[i]));
        }
        sort(line.begin(), line.end());
        build(, vec.size() + , );
        double ans = ;
        for(int i=; i<line.size(); ++ i)
        {
            if(i != )
                ans += (line[i].h - line[i-].h)*tree[].len;
            updata(line[i].l, line[i].r, , line[i].flag);
        }
        printf("Test case #%d\nTotal explored area: %.2f\n\n", ++ cases, ans);
    }
}