10分代码:

#include <iostream>
#include <cmath>
#include <algorithm>

using namespace std;

int m, n, ans;
int a[100001];

int christ(int l, int r, int key) {
	int mid;
	while (l + 1 < r) {
		mid = (l + r) >> 1;
		if (a[mid] <= key) l = mid;
		else r = mid;
	}
	if (key - a[l] <= a[r] - key) return a[l];
	else return a[r];
}

int main() {
	cin >> m >> n;
	for (int i = 1; i <= m; i ++ ) cin >> a[i];
	sort(a + 1, a + n + 1);
	for (int i = 1; i <= n; i ++ ) {
		int b;
		cin >> b;
		int t = christ(1, m, b);
		ans += abs(t - b);
	}
	cout << ans << endl;
    return 0;
}

求大佬指教，谢谢