题解 | #圣诞节糖果#

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

const int N = 1e5 + 10;
int a[N];

void solve()
{
	int n, p;
	cin >> n >> p;
	for(int i = 0; i < n; i ++ )
	{
		int x;
		cin >> x;
		a[i] = x % p;
	}
	sort(a, a + n);
	
	int res = 0;
	for(int i = 0; i < n; i ++ )
	{
		int x = p - a[i] - 1;
		int j = upper_bound(a, a + n, x) - a;
		j -- ;
		
		if(i != j && j > 0 && j < n)
		    res = max(res, a[i] + a[j]);
		
		x = p * 2 - a[i] - 1;
		j = upper_bound(a, a + n, x) - a;
		j -- ;
	    
		if(i != j && j > 0 && j < n)
		    res = max(res, (a[i] + a[j]) % p);
	}
	cout << res << endl;
}

signed main()
{
    int tt;
    cin >> tt;
    while(tt -- )
    {
    	solve();
	}
	return 0;
}