[Codeforces Round472C] Three-level Laser

[题目链接]

https://codeforces.com/contest/957/problem/C

[算法]

二分

注意精度问题

时间复杂度 ：O（NlogN)

[代码]

#include<bits/stdc++.h>
using namespace std;
const double eps = 1e-;
const int MAXN = 1e5 + ;
 
int n,m;
int a[MAXN];
double ans;
bool ok;
 
template <typename T> inline void read(T &x)
{
    int f = ; x = ;
    char c = getchar();
    for (; !isdigit(c); c = getchar()) { if (c == '-') f = -f; }
    for (; isdigit(c); c = getchar()) x = (x << ) + (x << ) + c - '';
    x *= f;
}
template <typename T> inline void write(T x)
{
    if (x < )
    {
        putchar('-');
        x = -x;
    }
    if (x > ) write(x/);
    putchar(x%+'');
}
template <typename T> inline void writeln(T x)
{
    write(x);
    puts("");
}
 
int main()
{
 
        read(n); read(m);
        for (int i = ; i <= n; i++) read(a[i]);
        ans = 0.0; ok = false;
        for (int i = ; i <= n; i++)
        {
                int l = i +  , r = n , pos = -;
                while (l <= r)
                {
                        int mid = (l + r) >> ;
                        if (a[mid] - a[i] <= m)
                        {
                                pos = mid;
                                l = mid + ;
                        } else r = mid - ;
                }
                if (pos == - || pos == i + ) continue;
                if ((1.0 * (a[pos] - a[i + ]) / (a[pos] - a[i]) - ans) > eps)
                        ans = 1.0 * (a[pos] - a[i + ]) / (a[pos] - a[i]);
                ok = true;
        }
        if (!ok) printf("-1\n");
        else printf("%.10lf\n",ans);
 
        return ;
 
}