RT，赛时坐牢2h，请问是假了还是写挂了。

record

加了一点注释

#include<bits/stdc++.h>
using namespace std;

inline char gc()
{
    static char BB[1000000], * S = BB, * T = BB;
    return (S == T) && (T = (S = BB) + fread(BB, 1, 1000000, stdin), S == T) ? EOF : *S++;
}

template <typename T>
T read(){
    T x = 0, f = 1;
    char ch = gc();
    while(ch < '0' || ch > '9'){if (ch == '-') f = -1; ch = gc();}
    while(ch >= '0' && ch <= '9'){x = x * 10 + ch - '0'; ch = gc();}
    return x * f;
}

template <> double read<double> (){
    double x = 0;
    int f = 1;
    char ch = gc();
    while(ch < '0' || ch > '9'){if (ch == '-') f = -1; ch = gc();}
    while(ch >= '0' && ch <= '9'){x = x * double(10) + double(ch - '0'); ch = gc();}
    if(ch == '.'){
        ch = gc();
        double now = 1;
        while(ch >= '0' && ch <= '9'){
            now /= double(10);
            x = x + now * double(ch - '0');
            ch = gc();
        }
    }
    return x * f;
}

template <typename T>
void read(T & t){
    T x = 0, f = 1;
    char ch = gc();
    while(ch < '0' || ch > '9'){if (ch == '-') f = -1; ch = gc();}
    while(ch >= '0' && ch <= '9'){x = x * 10 + ch - '0'; ch = gc();}
    t = x * f;
}

template <> void read<double> (double & t){
    double x = 0;
    int f = 1;
    char ch = gc();
    while(ch < '0' || ch > '9'){if (ch == '-') f = -1; ch = gc();}
    while(ch >= '0' && ch <= '9'){x = x * double(10) + double(ch - '0'); ch = gc();}
    if(ch == '.'){
        ch = gc();
        double now = 1;
        while(ch >= '0' && ch <= '9'){
            now /= double(10);
            x = x + now * double(ch - '0');
            ch = gc();
        }
    }
    t = x * f;
}

template <typename T, typename...Args>
void read(T & value, Args & ... args){
    read(value);
    read(args...);
}


template <typename T>
void sprint(T x, int w = 0){
    if(x < 0){putchar('-'); x = -x;}
    char ch[20];
    int t = 0;
    while(x){
        ch[++t] = x % 10 + '0';
        x /= 10;
    }
    for(int i = t; i >= 1; i--){
        putchar(ch[i]);
    }
    if(t == 0) putchar('0');
    switch(w){
        case 1:{
            putchar(' ');
            break;
        }
        case 2:{
            putchar('\n');
            break;
        }
        default:{
            break;
        }
    }
}

template<typename T>
void mprint(const T & value){
    T x = value;
    sprint(x, 2);
}

template<typename T, typename ...Args>
void mprint(const T & value, const Args & ... args){
    T x = value;
    sprint(x, 1);
    mprint(args...);
}

const int N = 1005;
const double eps = 1e-6;
int n, x[N];
struct spec{
    int tot;
    pair<double, double> data[N];
    spec(){
        tot = 0;
    }
    spec & operator=(const spec & B){
        tot = B.tot;
        for(int i = 1; i <= tot; i++) data[i] = B.data[i];
        return *this;
    }
}pre, now;//存每个x_i的答案的区间
//计算x_i的答案的区间
void make_spec(spec & sp, int i){
    sp.tot = 0;
    for(int k = i; k >= 1; k--){
        sp.data[++sp.tot].first = double(i) / double(k);
        sp.data[sp.tot].second = double(i + 1) / double(k);
    }
}
void print(spec & sp){
    for(int i = 1; i <= sp.tot; i++){
        printf("<%.7lf %.7lf> ", sp.data[i].first, sp.data[i].second);
    }
    putchar('\n');
}
//合并区间
spec Union(const spec & A, const spec & B){
    spec ret;
    for(int i = 1, j = 1; i <= A.tot; i++){
        while(j <= B.tot && A.data[i].first > B.data[j].second) ++j;
        while(j <= B.tot && A.data[i].second > B.data[j].first){
            ++ret.tot;
            ret.data[ret.tot] = make_pair(max(A.data[i].first, B.data[j].first), min(A.data[i].second, B.data[j].second)); 
            if(ret.data[ret.tot].second < ret.data[ret.tot].first + eps) --ret.tot;
            //printf("%d %.7lf %.7lf %.7lf %.7lf\n", ret.tot, A.data[i].first, B.data[j].first, A.data[i].second, B.data[j].second);
            ++j;
        }
        if(j > B.tot) break; 
    }
    return ret;
}
int main(){
    read(n);
    for(int i = 1; i <= n; i++){
        read(x[i]);
    }
    make_spec(pre, x[1]);
    //print(pre);
    for(int i = 2; i <= n; i++){
        make_spec(now, x[i]);
        //print(now);
        pre = Union(pre, now);//把每个now合并到pre上
        //print(pre);
    }
    //print(pre);
    for(int i = pre.tot; i >= 1; i--){
        if(pre.data[i].second - pre.data[i].first > eps){
            printf("%.7lf\n", pre.data[i].second);
            break;
        }
    }
    return 0;
}