Codeforces 51c (three base stations)

[Description]

There are many houses on both sides of the expressway. Each house has its own coordinates. Now, given three base stations, each base station has a corresponding coverage radius D, now I want to make the base station cover all the houses. How should I build the base station and what is the minimum coverage radius?

[Solution ideas]

We can divide the coverage radius of the base station into two parts, and the left endpoint l of the two parts is 0, the right range endpoint R is C [N]-C [1], that is, the range occupied by all houses. In this way, you can calculate the base station radius. It is a little tricky to find the coordinates of the base station. You can see the following code.

AC code]

1 # include <iostream> 2 # include <cstdio> 3 # include <algorithm> 4 using namespace STD; 5 # define Max 2*100000 + 5 6 int C [Max]; 7 int ans [3]; 8 int N; 9 int fnext (int x) // calculate the next coordinate 10 {11 int L = 1, R = n + 1; 12 INT mid = (L + r)/2; 13 while (L <r) 14 {15 if (C [Mid] <= X) L = Mid + 1; 16 else r = mid; 17 mid = (L + r)/2; 18} 19 return mid; 20} 21 int OK (INT X) 22 {23 int z = 1; 24 for (INT I = 0; I <3; I ++) 25 {26 z = fnext (C [Z] + x ); // here is the next house on the right side of the house covered by a base station 27 ans [I] = z; // store Z to conveniently find the base station coordinates 28 If (z> = n + 1) return 1; 29} 30 return 0; 31} 32 int main () 33 {34 while (CIN> N) 35 {36 for (INT I = 1; I <n + 1; I ++) 37 {38 CIN> C [I]; 39} 40 sort (C + 1, C + 1 + n ); 41 int r = C [N]-C [1]; 42 int L = 0, mid = (L + r)/2; 43 while (L <R) 44 {45 if (OK (MID) r = mid; 46 else47 L = Mid + 1; 48 mid = (R + l)/2; 49} 50 OK (l); 51 double radious = L * 1.0/2.0; 52 double radar1 = (C [ans [0]-1] + C [1]) * 1.0/2.0; 53 double radar2 = (C [ans [1]-1] + C [ans [0]) * 1.0/2.0; 54 double radar3 = (C [ans [2]-1] + C [ans [1]) * 1.0/2.0; 55 printf ("%. 6f \ n ", radious); 56 printf (" %. 6f ", radar1); 57 printf (" %. 6f ", radar2); 58 printf (" %. 6f \ n ", radar3); 59} 60 return 0; 61 62}