POJ 2932 (扫描线)

最新推荐文章于 2020-06-12 22:52:36 发布

morejarphone

最新推荐文章于 2020-06-12 22:52:36 发布

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分类专栏：扫描线

本文链接：https://blog.youkuaiyun.com/morejarphone/article/details/50110943

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本文介绍了一种用于判断圆是否在另一个圆内部的算法，包括输入参数、核心逻辑和输出结果的详细说明。

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#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <iostream>
using namespace std;
#define maxn 81111
#define pb push_back
#define mp make_pair

double x[maxn], y[maxn], r[maxn];
int n;

bool in (int i, int j) { //判断圆i在不在圆j里面
    double xx = x[i]-x[j], yy = y[i]-y[j];
    return sqrt (xx*xx + yy*yy) + r[i] < r[j];
}

int main () {
    //freopen ("in", "r", stdin);
    while (scanf ("%d", &n) == 1) {
        for (int i = 1; i <= n; i++) {
            scanf ("%lf%lf%lf", &r[i], &x[i], &y[i]);
        }
        vector <pair<double, int> > a;
        for (int i = 1; i <= n; i++) {
            a.pb (mp (x[i]-r[i], i));
            a.pb (mp (x[i]+r[i], i+n));
        }
        sort (a.begin (), a.end ());

        set <pair<double, int> > gg; gg.clear ();
        vector <int> ans; ans.clear ();

        for (int i = 0; i < a.size (); i++) {
            int id = a[i].second;
            if (id <= n) { //左边界
                set <pair<double, int> >:: iterator it = gg.lower_bound (mp (y[id], id));
                if (it != gg.end () && in (id, it->second))
                    continue;
                if (it != gg.begin () && in (id, (--it)->second))
                    continue;
                ans.pb (id);
                gg.insert (mp (y[id], id));
            }
            else {
                id -= n;
                gg.erase (mp (y[id], id));
            }
        }

        sort (ans.begin (), ans.end ());
        printf ("%d\n", ans.size ());
        for (int i = 0; i < ans.size (); i++) {
            printf ("%d%c", ans[i], (i+1 == ans.size () ? '\n' : ' '));
        }
    }
    return 0;
}