9.10(Ваня и фонари)

#include <string.h>
#include<cstdlib>
#include<ctime>
#include <vector>
#include <algorithm>
#include <iomanip>

using namespace std;



int main()
{
    int n,l;
    double buff,Max=0,dist;
    vector <double> v;
    cin>>n>>l;
    for (int i=0;i<n;i++)
    {
        cin>>buff;
        v.push_back(buff);
    }

    sort(v.begin(),v.end());

    for (int i=0;i<n-1;i++)
    {
        dist=v[i+1]-v[i];
        if (dist>Max) Max=dist;
    }
    Max=Max/2;
    if (v[0]>Max) {Max=v[0];}
    if (l-v[n-1]>Max) {Max=l-v[n-1];}
    cout<<fixed;
        cout<<setprecision(9)<<Max;
    return 0;
}