#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define el << "\n"
 
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
 
int t;
cin >> t;
while(t--){
    ll n,m;
    cin>>n>>m;
    ll a[1000005];
    for(ll i=0;i<n;i++){
        cin>>a[i];
    }
 
    sort(a,a+n);
 
    ll y = 0;
    for(ll i=0;i<n;i+=2){
        ll w = a[i] - a[i+1];
        if(w < 0){
            w = -w;
        }
        y += w;
    }
 
    cout << y el;
}
 
return 0;
}

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Mwo0IDEwCjEgNCA3IDkKNiAyMAoyIDUgNiAxMSAxMyAxNQo4IDEwMAoxMCAxMiAxMCAxNSAyMCAxOCAyMSAyNQo=

3
4 10
1 4 7 9
6 20
2 5 6 11 13 15
8 100
10 12 10 15 20 18 21 25