我不理解。卡了两天，#1WA

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int m = 0, n = 0, t = 0, sum = 0, b = 0, l = 0, r = 0, mid = 0;
    cin >> m >> n;
    int a[m], c[n] = {0};
    for (int i = 0; i < m; i++)
    {
        cin >> a[i];
    }
    sort(a, a + m);
    for (int i = 0; i < n; i++)
    {
        cin >> b;
        t = 1000001;
        l = 0;
        r = m - 1;
        while(l <= r)
        {
            mid = (l + r) / 2;
            if(a[mid] == b)
            {
                t = 0;
                break;
            }
            else if(a[mid] < b)
            {
                t = min(abs(a[mid] - b), t);
                l = mid + 1;
            }
            else if(a[mid] > b)
            {
                t = min(abs(a[mid] - b), t);
                r = mid - 1;
            }
        }
        c[i] = t;
    }
    sort(c, c + n);
    for (int i = 0; i < n; i++)
    {
        sum += c[i];
    }
    cout << sum;
    return 0;
}

求大佬解答！！！