POJ_1151 Atlantis（线段树）

　　/*线段树扫描线问题，感觉可以作为这类问题的模板。问过师兄以后才过的。。。

按y轴建线段树。*/

struct node{
    int l, r, c;    //c表示被覆盖的情况，不为0表示被覆盖
    double sum, len;    //len表示当前段的长度，sum表示有效长度。就是可以计入求面积的长度
}node[N<<2];

struct line{
    double x;　　//记录x坐标
    double y1;   
    double y2;    //y1，y2用来记录平行y轴的线段的两个端点，
    int flag;    //标记是左边的边还是右边的边
}l[N];

//My Code:

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#define L(t) t << 1
#define R(t) t << 1 | 1

using namespace std;

const int N = 210;

struct node{
    int l, r, c;
    double sum, len;
}node[N<<2];

struct line{
    double x;
    double y1;
    double y2;
    int flag;
}l[N];

double y[N];

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

void creat(int t, int l, int r){
    node[t].l = l;
    node[t].r = r;
    node[t].c = 0;
    node[t].sum = 0;
    node[t].len = y[r] - y[l];
    if(l + 1 == r)    return ;
    int mid = (l + r) >> 1;
    creat(L(t), l, mid);
    creat(R(t), mid, r);
}

void updata_sum(int t){
    if(node[t].c > 0)    node[t].sum = node[t].len;
    else if(node[t].r != node[t].l + 1)    node[t].sum = node[L(t)].sum + node[R(t)].sum;
    else    node[t].sum = 0;
}

void updata(int t, int l, int r, int c){
    if(node[t].l == l && node[t].r == r){
        if(c)    node[t].c ++;
        else    node[t].c --;
        updata_sum(t);
        return ;
    }
    int mid = (node[t].l + node[t].r) >> 1;
    if(l >= mid)    updata(R(t), l, r, c);
    else if(r <= mid)    updata(L(t), l, r, c);
    else{
        updata(L(t), l, mid, c);
        updata(R(t), mid, r, c);
    }
    updata_sum(t);
}

int find(double key, int n){
    int l = 1, r = n, mid;
    while(l <= r){
        mid = (l + r) >> 1;
        if(y[mid] == key)    return mid;
        else if(y[mid] > key)    r = mid-1;
        else    l = mid + 1;
    }
    return 0;
}

int main(){
    //freopen("data.in", "r", stdin);

    int t, n, m, i, cas = 0;
    double x1, x2, y1, y2, ans;
    while(scanf("%d", &t), t){
        m = 1;
        while(t--){
            scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2);
            y[m] = y1; l[m].x = x1; l[m].y1 = y1; l[m].y2 = y2; l[m].flag = 1; m++;
             y[m] = y2; l[m].x = x2; l[m].y1 = y1; l[m].y2 = y2; l[m].flag = 0; m++;
        }
        sort(y+1, y+m);
        sort(l+1, l+m, cmp);
        m--; n = 2;
        for(i = 1; i < m; i++)
            if(y[i] != y[i+1])    y[n++] = y[i+1];
        n--; creat(1, 1, n);
        for(ans = 0, i = 1; i < m; i++){
            if(l[i].flag)    updata(1, find(l[i].y1, n), find(l[i].y2, n), 1);
            else    updata(1, find(l[i].y1, n), find(l[i].y2, n), 0);
            ans += node[1].sum * (l[i+1].x - l[i].x);
        }
        printf("Test case #%d\nTotal explored area: %.2lf\n\n", ++cas, ans);
    }
    return 0;
}