数学二分——cf700A

 二分答案

#include<bits/stdc++.h>
using namespace std;
#define ll long long
int n,l,v1,v2,k;
double judge(double mid){//在mid时间内走完 
    if(mid*v2<l)return 0;
    double t=mid-(v2*mid-l)/(v2-v1);//每人坐车t分钟 
    double rt=t*(v2-v1)/(v1+v2);//回去的时间
    int num=n/k;//送的批数
    if(n%k)num++;
    double tot=num*t+(num-1)*rt;
    if(tot<mid)return 1;
    return 0; 
}

int main(){
    cin>>n>>l>>v1>>v2>>k;
    double L=0,R=1e10,ans,mid;
    while(R-L>1e-6){
        mid=(L+R)/2;
        if(judge(mid))
            ans=mid,R=mid;
        else L=mid;
    }
    printf("%.10lf\n",ans);
}