The pain of Xiao Sha

Their thinking   ： You can use binary search , Found   The current value adds up to the maximum value  

#include"bits/stdc++.h"
#define ll long long
#define pi pair<int,int>
#define inf 0x3f3f3f3f
#define  _for(i,a,b) for(int i=a;i<=b;i++)
#define  for_(i,a,b) for(int i=a;i<b;i++)
#define _fr(i,a,b) for(int i=a;i>=b;i--)
#define fr_(i,a,b) for(int i=a;i>b;i--)
#define IOS ios::sync_with_stdio(false),cin.tie(0),cout.tie(0)
using namespace std;
const int N = 1e6+5;
const ll mod = 1e9+7;
const double lp=1.000000011;
map<int,int>mp;
ll arr[N];
void solve(){
    ll n,m,x;
    cin >> n >> m;
    _for(i,1,n) cin >> arr[i],arr[i]%=m;
    sort(arr+1,arr+1+n);
    ll res = (arr[n]+arr[n-1])%m;
    _for(i,1,n){
        x = lower_bound(arr+i+1,arr+n,m-arr[i])-arr;
        if(x != i+1) res = max(res,(arr[i]+arr[x-1])%m);
    }
    cout << res << endl;

}

int main()
{
    IOS;
    solve();
    return 0;
}