Ternary search

double func(double x){
    return -1*1*x*x + 2*x +3;
}


double ts(double start, double end){
    double l = start, r = end;

    for(int i=0; i<200; i++) {
      double l1 = (l*2+r)/3;
      double l2 = (l+2*r)/3;
      //cout<<l1<<" "<<l2<<endl;
      if(func(l1) > func(l2)) r = l2; else l = l1;
      }

     double x = l;
    return func(x);
}

int tsi(){
    int lo = -1, hi = n;
    while (hi - lo > 1){
        int mid = (hi + lo)>>1;
        if (f(mid) > f(mid + 1))
            hi = mid;
        else
            lo = mid;
    }
    return lo + 1;
}