60分，求助大佬

#include <bits/stdc++.h>
using namespace std;
long long m,n,sum=0;
long long a[100005],b[100005],bb[100005],u[100005];

void binarysearch(long long x,long long f)
{
    long long left=0,right=m-1;
    while(left<=right)
    { long long mid=(left+right)/2;
        if(x==a[mid])
        {   
            bb[f]=a[mid];
            u[f]=0;
            return;
        }
        else if(x<a[mid])
        {
            right=mid-1;
        }
        else
        {
            left=mid+1;
        };
    }
    //cout<<left<<" "<<right<<endl;
    if(right==-1)
    {
        u[f]=a[0]-b[f];
        //cout<<u[f]<<endl;
    }
    if(left==m)
    {
        u[f]=a[m-1]-b[f];
    }
    else
    {

    for (long long j=right;j<=left;j++)
    {
        if (abs(a[j]-b[f])<u[f])
        {
           u[f]=abs(a[j]-b[f]);
           //cout<<u[f]<<endl;
        }
    }
}
    return;
}
int main ()
{   memset(u,9999999,sizeof(u));
    memset(bb,0,sizeof(bb));
    cin>>m>>n;
    for (int i=0;i<m;i++)
      cin>>a[i];
    for (int i=1;i<=n;i++)
    {
        cin>>b[i];
    }
    sort(a,a+m);
    for (int i=1;i<=n;i++)
    {
        binarysearch(b[i],i);
    }

    for (int i=1;i<=n;i++)
    {  
        sum+=u[i];
    }
    cout<<sum;
}