【二分】Garland

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坑爹只是小事

#include <iostream>#include <cstdio>#include <cstdlib>#include <algorithm>#include <cstring>#include <ctime>#include <cmath>#define mxn 1000+10#define loc#define mx 1e20#define df 1e-10using namespace std;int n;double A;double h[mxn];bool ck(double x){     memset(h,0,sizeof(h));     h[1]=A,h[2]=x;     for (int i=2;i<=n;++i)     {         h[i+1]=2*h[i]+2-h[i-1];         if (h[i]<0) return false;     }          return true;}void bs(){     double l=0,r=A,m,min=mx;     while (l+df<r)     {           m=(l+r)/2;           if (!ck(m)) l=m;           else           {               r=m;               if (h[n]<min) min=h[n];           }     }          printf("%.2lf",min);}int main(){    freopen("garland.in","r",stdin);    freopen("garland.out","w",stdout);        scanf("%d%lf",&n,&A);        bs();    return 0;}