90pts求助

#include <bits/stdc++.h>

using namespace std;

bool cmp(int a,int b)
{
    return a>b;
}
int main()
{
    int m,n;
    cin >> m >> n;
    const int M = m,N = n;
    int school[M],student[N];
    for(int i = 0;i < m;i++)
        cin >> school[i];
    for(int i = 0;i < n;i++)
        cin >> student[i];
    sort(school,school+m);
    int lis[N];
    for(int i = 0;i < n;i++)
    {
        lis[i]=abs(student[i]-*lower_bound(school,school+m,student[i]));
    }
    sort(school,school+m,cmp);
    unsigned long long sum = 0;
    for(int i = 0;i < n;i++)
    {
        int temp = abs(student[i]-*lower_bound(school,school+m,student[i],cmp));
        if(temp < lis[i])
            lis[i]=temp;
        sum+=lis[i];
    }
    cout << sum;
    return 0;
}