Submission #1066728

#	Time	Username	Problem	Language	Result	Execution time	Memory
1066728		Oz121	Mobile (BOI12_mobile)	Java	13 / 100	1067 ms	131072 KiB

mobile

import java.io.*;
import java.util.*;
public class mobile {
    public static int num; public static double[][] arr;
    public static void main(String[] args) throws IOException {
        BufferedReader scan = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer l1 = new StringTokenizer(scan.readLine()); num = Integer.parseInt(l1.nextToken()); int L = Integer.parseInt(l1.nextToken()); arr = new double[num][2];
        for (int i = 0;i<num;i++) {
            StringTokenizer st = new StringTokenizer(scan.readLine());
            arr[i][0] = Integer.parseInt(st.nextToken());
            arr[i][1] = Integer.parseInt(st.nextToken());
        }

        double l = 0; double h = Math.pow(10,9);
        while (h-l>Math.pow(10,-3)) {
            double mid = (l+h)/2; boolean work = true;
            ArrayList<Pair> endpoints = getEndpoints(mid);
            endpoints.sort(Comparator.comparingDouble(i -> i.l));

            /*System.out.println("  "+mid);
            for (int i = 0;i<endpoints.size();i++) {
                System.out.println(endpoints.get(i).l+" "+endpoints.get(i).r);
            }
            System.out.println("--------");*/

            if (endpoints.isEmpty()) {l = mid; continue;}

            double left = endpoints.get(0).l; double right = endpoints.get(0).r;
            for (int i = 1;i<endpoints.size();i++) {
                if (endpoints.get(i).l>right) work = false;
                left = Math.min(left, endpoints.get(i).l); right = Math.max(right, endpoints.get(i).r);
            }
            work = (work)&&(left<=0&&right>=L);

            if (work) h = mid;
            else l = mid;
        }

        System.out.println((l+h)/2);
    }

    public static ArrayList<Pair> getEndpoints (double r) {
        ArrayList<Pair> endpoints = new ArrayList<>();
        for (int i = 0;i<num;i++) {
            if (r*r-arr[i][1]*arr[i][1]<0) continue;
            endpoints.add(new Pair(arr[i][0]-Math.sqrt(r*r-arr[i][1]*arr[i][1]),
                            arr[i][0]+Math.sqrt(r*r-arr[i][1]*arr[i][1])));
        }
        return endpoints;
    }

    public static class Pair {
        double l; double r;
        public Pair (double l, double r) {
            this.l = l; this.r = r;
        }
    }
}

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