1399 C. Boats Competition.cpp

/*
problem link: https://codeforces.com/contest/1399/problem/C
my solution on codeforces :https://codeforces.com/contest/1399/submission/174913285
problem name: C. Boats Competition
status: accepted
author: lilian_steven   or LELLO 
*/
#include <bits/stdc++.h>
#include <iostream>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <cmath>
#include <unordered_map>
#include <algorithm>
#include <iomanip>
#include <bitset>
#include <utility>
#include <string>
#include <cctype>
#include <iomanip>
#include <numeric> // for NTH
#define bye return;
#define ll long long
#define lli long long int
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) ((x).size())
#define ison(num, bit) (num & (1 << bit))
#define setoff(num, bit) (num ^= (1 << bit)) // iff (num &(1<<bit))
#define flipbit(num, bit) (num ^= (1 << bit))
#define setbit(num, bit) (num |= (1 << bit))
#define clearbit(num, bit) (num &= ~(1 << bit))
#define pop_count(num) __builtin_popcount(num)
#define Num_of_Digits(n) ((ll)log10(n) + 1)
#define ceill(n, m) (((n) / (m)) + ((n) % (m) ? 1 : 0))
#define lastOne(x) (__builtin_clzll(x))
#define Pi  3.14159265358979323846264
#define sin(a) sin((a)*PI/180)
#define cos(a) cos((a)*PI/180)
ll sgn(ll x){ if(x > 0) return 1; if(x < 0) return -1; return 0;}
ll gcd(ll a, ll b){if(b == 0) return a; return gcd(b, a%b);}
ll lcm(ll a, ll b){return a/gcd(a, b)*b;}
using namespace std;
void AC() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); // or cin.tie(NULL)
    cout.tie(nullptr);  // or cout.tie(0)
    // #ifndef ONLINE_JUDGE
    //     freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
    // #endif
}
bool cmp(pair<int,int>&a, pair<int,int>&b){
    if(a.first == b.first){
        return a.second > b.second;
    }
    return a.first < b.first;
}
// int dx[] = {1,-1,0,0} , dy[] = {0,0,1,-1};  // 4 Direction
// int dx[] = {1,-1,0,0,1,1,-1,-1}  , dy[] = {0,0,1,-1,1,-1,1,-1};  // 8 Direction
// int dx[] = {1,-1,1,-1,2,2,-2,-2} ,  dy[] = {2,2,-2,-2,1,-1,1,-1}; // Knight Direction
// int dx[] = {2,-2,1,1,-1,-1} ,  dy[] = {0,0,1,-1,1,-1}; // Hexagonal Direction

void LELLO()
{
    int n ; cin >> n ;
    vector<int> vc(n) ;
    map<int, vector<pair<int , int> >> mp ;
    for(int i = 0; i < n ; i++){
        cin >> vc[i];
    }
    for (int i = 0; i < n-1; i++)
    {
        for (int j = i+1; j < n; j++)
        {
            mp[vc[i]+vc[j]].push_back({i , j});
        }
        
    }
    int mx = 0 ;
    for(auto& it : mp){
        unordered_set <int> st;
        int j = 1 ;
        for(int i = 0; i < it.second.size(); i++){
            if(st.find(it.second[i].first) == st.end() && st.find(it.second[i].second) ==st.end()){
                st.insert(it.second[i].first);
                st.insert(it.second[i].second);
            }
        }
            int co = st.size()/2;
            mx = max( co , mx);
    }
    cout<< mx <<endl;
    bye
}
void driver(ll t)
{
    while (t--) LELLO();
}
signed main()
{
    AC();
    // sieve();
    ll test ; cin >> test ;
    driver(test);
}