对y轴建一棵线段树

例题

Atlantis

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 210;

struct edge {
    double x, y1, y2;
    int state;
    edge() {
    }
    edge(double a, double b, double c, int d) : x(a), y1(b), y2(c), state(d) {
    }
    bool operator < (const edge &t) const {
        return x < t.x;
    }
} line[N];

double v[N];
double len[N * 4];
int add[N * 4];
int n;
int casei;

void pushup(int k, int l, int r) {
    if (add[k])
        len[k] = v[r] - v[l];
    else if (r - l == 1)
        len[k] = 0;
    else {
        int ls = k * 2 + 1;
        int rs = k * 2 + 2;
        len[k] = len[ls] + len[rs];
    }
}

void update_tree(int start, int end, int val, int k, int l, int r) {
    if (end <= l || r <= start)
        return;

    if (start <= l && r <= end) {
        add[k] += val;
        pushup(k, l, r);
        return;
    }

    int mid = (l + r) / 2;
    int ls = k * 2 + 1;
    int rs = k * 2 + 2;
    update_tree(start, end, val, ls, l, mid);
    update_tree(start, end, val, rs, mid, r);
    pushup(k, l, r);
}

int main() {
    while (~scanf("%d", &n)) {
        if (n == 0)
            break;
        double a, b, c, d;

        for (int i = 0; i < n; i ++ ) {

            scanf("%lf%lf%lf%lf", &a, &b, &c, &d);
            line[i] = edge(a, b, d, 1);
            line[i + n] = edge(c, b, d, -1);
            v[i] = b;
            v[i + n] = d;
        }

        n *= 2;
        sort(line, line + n);
        sort(v, v + n);
        int vn = unique(v, v + n) - v;
        double ans = 0;

        for (int i = 0; i < n; i ++ ) {

            if (i)
                ans += (line[i].x - line[i - 1].x) * len[0];
            int L = lower_bound(v, v + vn, line[i].y1) - v;
            int R = lower_bound(v, v + vn, line[i].y2) - v;
            update_tree(L, R, line[i].state, 0, 0, n);
        }

        printf("Test case #%d\n", ++ casei);
        printf("Total explored area: %.2lf\n\n", ans);
    }

    return 0;
}