1121B-Mike_and_Children.cpp

/*
    written by Pankaj Kumar.
    country:-INDIA
*/
#include <bits/stdc++.h>
using namespace std;
typedef long long ll ;
typedef set<pair<int,int>> spi;
typedef set<pair<ll,ll>> spl;
typedef vector<pair<int,int>> vpi;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<pair<ll,ll>> vpl;
typedef vector<string> vs;
typedef map<int,int>mi;
typedef map<ll,ll> ml;
typedef set<string> ss;
typedef set<char>sc;
typedef set<int> si;
typedef set<ll> sl;
#define pan cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(0);
// define values.
#define mod 1e9+7LL
#define phi 1.618
/* Bit-Stuff */
#define get_set_bits(a) (__builtin_popcount(a))
#define get_set_bitsll(a) ( __builtin_popcountll(a))
#define get_trail_zero(a) (__builtin_ctz(a))
#define get_lead_zero(a) (__builtin_clz(a))
#define get_parity(a) (__builtin_parity(a))
/*  Abbrevations  */
#define ff first
#define ss second
#define mp make_pair
#define line cout<<endl;
#define pb push_back
#define Endl "\n"
// loops
#define loop(i,start,end) for(ll i=ll(start);i<ll(end);i++)
#define loop0(num) for(ll i=0;i<ll(num);i++)
#define forin(arr,n) for(ll i=0;i<n;i++) cin>>arr[i];
// Some print
#define no cout<<"NO"<<endl;
#define yes cout<<"YES"<<endl;
#define cc ll test;cin>>test;while(test--)
// sort
#define all(V) (V).begin(),(V).end()
#define srt(V) sort(all(V))
#define srtGreat(V) sort(all(V),greater<ll>())
// function

ll power(ll x,ll y, ll p)  
{  
    ll res = 1;      
    x = x % p;             
    while (y > 0)  
    {    
        if (y & 1)  
            res = (res*x) % p;   
        y = y>>1; 
        x = (x*x) % p;  
    }  
    return res;  
} 
/* ascii value 
A=65,Z=90,a=97,z=122 1=49
*/
/*  -----------------------------------------------------------------------------------*/
// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);

int solve()
{
	ll n;
    cin>>n;
    vl v(2000001,0);
    vl a(n,0);
    forin(a,n);
    for(ll i=0;i<n;i++)
    {
        for(ll j=i+1;j<n;j++)
            v[a[i]+a[j]]++;
    }
    ll maxo=-1;
    for(ll i=1;i<200001;i++)
        maxo=max(maxo,v[i]);
    cout<<maxo<<endl;
	return 0;
}

int main()
{
	pan
	solve();
    // cc
    // {
    // 	solve();
    // }
}