求说明Subtask #1没过

#include<bits/stdc++.h>
using namespace std;
int m,n,mid,ans=0;
int a[1000005],b[1000005]; //a学校线，b学生线 
int main()
{
    cin>>n>>m;
    for (int i=1;i<=n;i++)
    {
        cin>>a[i];      
    }
    for (int i=1;i<=m;i++)
    {
        cin>>b[i];      
    }
    sort(a+1,a+n+1);//小到大 
    for (int i=1;i<=m;i++)
    {
        int l=0,r=n+1;//左右区间    
        while(l<r)
        {
            mid=(l+r)/2;
            if(a[mid]<=b[i]) l=mid+1;
            else r=mid;
        }
        if(b[i]<=a[1]) ans+=a[1]-b[i];
        else ans+=min(abs(a[l-1]-b[i]),abs(a[l]-b[i]));//求差 
    }
    cout<<ans; 
    return 0;
}