//二分求分界点
//整数二分找右分界点 
//即目标点后面的所有点满足条件
//返回值为第一个满足目标点的元素
int bsearch_1(int l,int r)
{
    while(l<r)
    {
        int mid = l+r>>1;
        if(check(mid)) r=mid;//向左边找
        else l =mid +1; 
    }
    return l;
 } 
//整数二分找左端点 
//即目标点前面的所有点满足条件
 int bserch_2(int l,int r)
 {
     while(l<r)
     {
         int mid =l+r+1>>1; //加一向上取整  
         if(check(mid))l=mid;
         else r =mid-1;
     }
     return l;
  } 
//浮点数二分求右边界
double bsearch_3(double l,double r)
{
    while(r-l>精度)
    {
        double mid =(l+r)/2;
        if(check(mid))r=mid;
        else l = mid;
     } 
     return l;
 } 

//浮点数求二分求左边界
double bserch_4(double l,double r)
 {
     while(r-l>精度)
     {
         double mid =l+r+1>>1; //加一向上取整  
         if(check(mid))l=mid;
         else r =mid;
     }
     return l;
  }