求问大佬

#include <cstdio>
#include <algorithm>
#include <cmath>
using namespace std;
int a[1000001];
int b[1000001];
int sum;
int cmp(int x,int y)
{
    return x<y;
}
int f(int x,int l,int r)
{
    while(l<=r)
    {
        int mid=(l+r)/2;
        if(x>a[mid])
        {
            l=mid+1;
        }else
        {
            r=mid-1;
        }
    }
    return l-1;
}
int main()
{
    int m,n;
    scanf("%d%d",&m,&n);
    for(int i=1;i<=m;i++)
    {
        scanf("%d",&a[i]);
    }
    for(int j=1;j<=n;j++)
    {
        scanf("%d",&b[j]);
    }
    sort(a+1,a+m+1,cmp);
    for(int i=1;i<m;i++)
    {
        int in=f(b[i],1,m);
        sum+=min(abs(b[i]-a[in]),abs(b[i]-a[in+1]));
    }
    printf("%d",sum);
    return 0;
}