#include <iostream>
using namespace std;
 
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
 
    int t;
    cin >> t;
 
    while (t--) {
        long long n, m;
        cin >> n >> m;
 
        long long a[1000005];
 
        for (long long i = 0; i < n; i++)
            cin >> a[i];
 
        for (long long i = 0; i < n - 1; i++) {
            for (long long j = i + 1; j < n; j++) {
                if (a[j] < a[i]) {
                    long long temp = a[i];
                    a[i] = a[j];
                    a[j] = temp;
                }
            }
        }
 
        long long ans = 0;
 
        for (long long i = 0; i < n; i += 2) {
            long long diff = a[i] - a[i + 1];
            if (diff < 0) diff = -diff;
            ans += diff;
        }
 
        cout << ans << "\n";
    }
 
    return 0;
}

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4 10
1 4 7 9
6 20
2 5 6 11 13 15
8 100
10 12 10 15 20 18 21 25