#include<bits/stdc++.h>
using namespace std;
//#pragma GCC optimize("Ofast")

#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define vtpl(x,y,z) vector<tuple<x,y,z>>
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
//const ll dy[9]={1,0,-1,0,1,1,-1,-1,0};
//const ll dx[9]={0,1,0,-1,1,-1,1,-1,0};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}


void solve(){
    ll n;cin >> n;
    ll l,k;cin >> l >> k;
    vl x(n);rep(i,n)cin >> x[i];
    sort(all(x));
    rep(i,n)x[i]*=2;l*=2;
    ll ok=l,ng=0;
    vl ord;
    rep(i,n)ord.emplace_back(x[i]-l);
    rep(i,n)ord.emplace_back(x[i]);
    rep(i,n)ord.emplace_back(x[i]+l);
    while(ok-ng>1){
        ll mid=(ok+ng)/2;
        bool judge=true;
        rep(i,n){
            ll p=(x[i]+mid+1)%l;
            ll left=p-mid,right=p+mid;
            if(upper_bound(all(ord),right)-lower_bound(all(ord),left)<k)judge=false;
        }
        if(judge)ok=mid;
        else ng=mid;
    }
    cout << (ok+1)/2 << endl;
}
int main(){
    ll q;cin >> q;
    while(q--)solve();
}