# [Codeforces492B] Vanya and Lanterns

## 描述 Description

Vanya walks late at night along a straight street of length l, lit by n lanterns. Consider the coordinate system with the beginning of the street corresponding to the point 0, and its end corresponding to the point l. Then the i-th lantern is at the point ai. The lantern lights all points of the street that are at the distance of at most d from it, where d is some positive number, common for all lanterns.

Vanya wonders: what is the minimum light radius d should the lanterns have to light the whole street?

## 输入格式 InputFormat

The first line contains two integers n, l (1 ≤ n ≤ 1000, 1 ≤ l ≤ 109) — the number of lanterns and the length of the street respectively.

The next line contains n integers ai (0 ≤ ai ≤ l). Multiple lanterns can be located at the same point. The lanterns may be located at the ends of the street.

## 输出格式 OutputFormat

Print the minimum light radius d, needed to light the whole street. The answer will be considered correct if its absolute or relative error doesn’t exceed 10 - 9.

7 15
15 5 3 7 9 14 0

2.5000000000

Codeforces 492B

## 代码 Code

``````#include <stdio.h>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
const int maxn=1005;
int i,j,t,n,m,l,r,k,z,y,x;
int a[maxn];
double ans;
int main()
{
scanf("%d%d",&n,&l);
for (i=1;i<=n;i++) scanf("%d",&a[i]);
sort(a+1,a+n+1);
ans=max((double)a,(double)(l-a[n]));
for (i=1;i<n;i++) ans=max(ans,(double)(a[i+1]-a[i])/2);
printf("%.10lf\n",ans);
return 0;
}``````