The first line of each test case is an integer n,
indicating the number of chips produced today. The next line has n integers s1,s2,..,sn,
separated with single space, indicating serial number of each chip.

1≤T≤1000
3≤n≤1000
0≤si≤109
There are at most 10 testcases
with n>100

#include <iostream>

#include <cstdio>

#include <cstring>

#include <cstdlib>

#include <queue>

#include <vector>

#include <algorithm>

#include <functional>

typedef long long ll;

using namespace std;

int a[1005];

struct node

{

    int number;

    int flag;

    int next[2];

    void ini()

    {

        next[0] = next[1] = 0;

        flag = 0;

    }

} pnode[1000005];

int root = 0;

int tot;

void inser(int x)

{

    int tt = root;

    for(int i = 30; i >= 0; i --)

    {

        int t;

        if(x & (1<<i))t = 1;

        else  t = 0;

        if(!pnode[tt].next[t])

        {

            pnode[tt].next[t] = ++tot;

            pnode[tot].number = t;

        }

        tt = pnode[tt].next[t];

        pnode[tt].flag++;

    }

}

void delet(int x)

{

    int tt = root;

    for(int i = 30; i >= 0; i--)

    {

        int t;

        if(x & (1<<i))t = 1;

        else  t = 0;

        tt = pnode[tt].next[t];

        pnode[tt].flag --;

    }

}

int query(int x)

{

    int tt = root;

    for(int i = 30; i >= 0; i--)

    {

        int t;

        if(x & (1<<i)) t = 1;

        else t = 0;

        if(t == 1)

        {

            int nex = pnode[tt].next[0];

            if(pnode[nex].flag > 0 && nex) tt = pnode[tt].next[0];

            else

            {

                tt = pnode[tt].next[1];

                x ^= (1<<i);

            }

        }

        else

        {

            int nex = pnode[tt].next[1];

            if(pnode[nex].flag > 0 && nex)

            {

                tt = pnode[tt].next[1];

                x ^= (1<<i);

            }

            else tt = pnode[tt].next[0];

        }

    }

    return x;

}

int main()

{

    int T,n;

    scanf("%d",&T);

    while(T--)

    {

        int ans = 0;

        scanf("%d",&n);

        tot = 0;

        for(int i = 0; i < n; i++)   scanf("%d",a+i);

        for(int i = 0; i < n; i++)   inser(a[i]);

        for(int i = 0; i < n; i++)

        {

            delet(a[i]);

            for(int j = i+1; j < n; j++)

            {

                delet(a[j]);

                ans = max(ans,query(a[i] + a[j]));

                inser(a[j]);

            }

            inser(a[i]);

        }

        for(int i = 0;i < tot;i++)

        {

            pnode[i].ini();

        }

        printf("%d\n",ans);

    }

    return 0;

}