#include<bits/stdc++.h>
using namespace std;
int a[100010],b[100010],m,n;
int main(){
	cin>>m>>n;
	long long l,r,ans=0,mid;
	for(int i=1;i<=m;i++)
		cin>>a[i];
	for(int i=1;i<=n;i++)
	    cin>>b[i];
	sort(a+1,a+1+m);
	for(int i=1;i<=n;i++){
	    long long l=0,r=n+1;
		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]));
	}
	cout<<ans;
	return 0;
}

为神马这样却对了

#include<bits/stdc++.h>
using namespace std;
int a[100010],b[100010];
int main()
{
	int n,m;
	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);
	long long ans=0;
	for(int i=1;i<=m;i++){
		int l=0,r=n+1;
		while(l<r){
			int 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]));
	}
	cout<<ans;
	return 0;
}