#include <bits/stdc++.h>
using namespace std;

#define sp putchar(' ')
#define en putchar('\n')
#define pb push_back
#define P 998244353
#define HP 1000000000000002097
#define N (int)(2e5+5)

int read(){ char ch=getchar();int x=0,f=1;while(ch>'9' || ch<'0'){if(ch=='-') f=-1;ch=getchar();}while(ch>='0' && ch<='9')x=(x<<1)+(x<<3)+(ch^48),ch=getchar();return x*f; }
void print(int x){ if(x<0) putchar('-'),x=-x;if(x>9)print(x/10);putchar(x%10+'0'); }

int n,k,a[N]; 
void solve()
{
	cin>>n>>k;
	for(int i=1;i<=n;i++) cin>>a[i];
	sort(a+1,a+1+n);
	int cnt=0;
	if(n%2==0){
		for(int i=2;i<=n;i+=2) cnt+=a[i]-a[i-1];
	}
	else{
		for(int i=3;i<=n;i+=2) cnt+=a[i]-a[i-1];
		cnt+=a[1];
	}
	if(cnt>=k) cout<<cnt-k<<"\n";
	else cout<<0<<"\n";
	for(int i=1;i<=n;i++) a[i]=0;
}
signed main()
{
	ios::sync_with_stdio(0);cin.tie(0),cout.tie(0);
	int T;
	cin>>T;
	while(T--){
		solve();
	}
	return 0;
}