ACM学习历程—POJ1151 Atlantis（扫描线 && 线段树）

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#define LL long long

using namespace std;

//线段树
//扫描线
const int maxn = 205;
struct node
{
    int lt, rt;
    double height;
    int num;
}tree[4*maxn];

struct Line
{
    double x;
    double y1, y2;
    bool isLeft;
}line[maxn];

bool cmp(Line a, Line b)
{
    return a.x < b.x;
}

double y[maxn];

//向上更新
void PushUp(int id)
{
    if(tree[id].num > 0)
    {
        tree[id].height = y[tree[id].rt] - y[tree[id].lt];
        return;
    }
    if(tree[id].lt+1 == tree[id].rt)
        tree[id].height = 0;
    else
        tree[id].height = tree[id<<1].height + tree[id<<1|1].height;
}

//建立线段树
void Build(int lt, int rt, int id)
{
    tree[id].lt = lt;
    tree[id].rt = rt;
    tree[id].height = 0;//每段的初值，根据题目要求
    tree[id].num = 0;
    if (lt+1 == rt)
    {
        //tree[id].val = 1;
        return;
    }
    int mid = (lt + rt) >> 1;
    Build(lt, mid, id<<1);
    Build(mid, rt, id<<1|1);
    //PushUp(id);
}

//寻找符合修改的区间通过判断num进行修改
void Updata(int id,Line p)
{
    if(p.y1 <= y[tree[id].lt] && p.y2 >= y[tree[id].rt])
    {
        if (p.isLeft > 0)
            tree[id].num++;
        else
            tree[id].num--;
        PushUp(id);
        return;
    }
    int mid = (tree[id].lt+tree[id].rt) >> 1;
    if (p.y1 < y[mid])
        Updata(id<<1, p);
    if (p.y2 > y[mid])
        Updata(id<<1|1, p);
    PushUp(id);
}

int n;

void Input()
{
    double x1, y1, x2, y2;
    int cnt = 1;
    for (int i = 0; i < n; ++i)
    {
        scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2);
        y[cnt] = y1;
        y[cnt+1] = y2;

        line[cnt].x = x1;
        line[cnt].y1 = y1;
        line[cnt].y2 = y2;
        line[cnt].isLeft = true;

        line[cnt+1].x = x2;
        line[cnt+1].y1 = y1;
        line[cnt+1].y2 = y2;
        line[cnt+1].isLeft = false;
        cnt += 2;
    }
    sort(y+1, y+1+2*n);
    sort(line+1, line+1+2*n, cmp);
    Build(1, 2*n, 1);
}

double Work()
{
    double ans = 0;
    Updata(1, line[1]);
    int len = 2*n;
    for (int i = 2; i <= len; ++i)
    {
        ans +=  (line[i].x-line[i-1].x) * tree[1].height;
        Updata(1, line[i]);
    }
    return ans;
}

int main()
{
    //freopen("test.in", "r", stdin);
    int times = 1;
    while (scanf("%d", &n) != EOF && n)
    {
        Input();
        double ans = Work();
        printf("Test case #%d\n", times);
        printf("Total explored area: %.2lf\n\n", ans);
        times++;
    }
    return 0;
}