1
while (l < r)
2
    {
3
        int mid = l + r >> 1;  //(l+r)/2
4
        if (check(mid))  r = mid;    // check()判断mid是否满足性质
5
        else l = mid + 1;
6
    }

1
  while (l < r)
2
    {
3
        int mid = l + r + 1 >> 1;  //(l+r+1)/2
4
        if (check(mid))  l = mid;
5
        else r = mid - 1;
6
    }

1
while(r-l>1e-5) //需要一个精度保证
2
{
3
  double mid = (l+r)/2;
4
  if(check(mid)) l=mid; //或r=mid;
5
  else r=mid; //或l=mid;
6
}