poj1151Atlantis扫描线

　　第一道扫描线。

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <climits>
#include <string>
#include <iostream>
#include <map>
#include <cstdlib>
#include <list>
#include <set>
#include <queue>
#include <stack>
using namespace std;
const int maxn = 4004;
double hash[maxn << 2];
int color[maxn << 2];
double sum[maxn << 2];
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1

struct Node
{
    int add; double l; double r; double h;
}node[maxn << 2];

int cmp(const Node&a, const Node &b)
{
    return a.h<b.h;
}

void up(int l, int r, int rt)
{
    if (color[rt]>0) sum[rt] = hash[r + 1] - hash[l];  //第 l个线段到 第r个线段的长度 = 第r+1个点与第l个点的距离
    //else if (l == r) sum[rt] = 0;
    else sum[rt] = sum[rt << 1] + sum[rt << 1 | 1];
}

void update(int L, int R, int add, int l, int r, int rt)
{
    if (L <= l&&r <= R){
        color[rt] += add;
        up(l, r, rt); return;
    }
    int mid = (l + r) >> 1;
    if (L <= mid) update(L, R, add, lson);
    if (R > mid) update(L, R, add, rson);
    up(l, r, rt);
}

int Bin(double key, double a[], int len)//  离散
{
    int l = 0; int r = len - 1;
    while (l <= r){
        int mid = (l + r) >> 1;
        if (a[mid] == key) return mid;
        if (a[mid] < key) l = mid + 1;
        else r = mid - 1;
    }
    return -1;
}

int main()
{
    int n;
    double a, b, c, d;
    int gg = 0;
    while (cin >> n, n){
        int m = 0;
        for (int i = 0; i < n; i++){
            cin >> a >> b >> c >> d;
            hash[m] = a;
            node[m].l = a; node[m].r = c; node[m].h = b; node[m++].add = 1;
            hash[m] = c;
            node[m].l = a; node[m].r = c; node[m].h = d; node[m++].add = -1;
        }
        int k = 0;
        sort(hash, hash + m);
        sort(node, node + m, cmp);
        k++;
        for (int i = 1; i<m; i++)
        if (hash[i] != hash[i - 1]) hash[k++] = hash[i];
        double ret = 0;
        for (int i = 0; i < m; i++){// 对最后一跟线扫完以后，sum与 color 都被清0了。 若是想手动初始化，就把 i<m  改为 i<m-1
            int L = Bin(node[i].l, hash, k);
            int R = Bin(node[i].r, hash, k) - 1;//点变线段 比如 1(1) 2 (2) 3 (3) 4
            update(L, R, node[i].add, 0, k - 1, 1);
            ret += sum[1] * (node[i + 1].h - node[i].h);
        }
        printf("Test case #%d
", ++gg);
        printf("Total explored area: %.2f
", ret);
        cout << endl;
    }
    return 0;
}