#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<string>
#define INF 100000000
using namespace std;
int n,mp[105][105],minn,maxx,link[105],mark[105],l,r,mid,p;
bool dfs(int x)
{
    for(int i=1;i<=n;i++)
    {
        if(mark[i]==-1&&mp[x][i]>=p&&mp[x][i]<=p+mid)
        {
            mark[i]=1;
            if(link[i]==-1||dfs(link[i]))
            {
                link[i]=x;
                return true;
            }
        }
    }
    return false;
}
bool check(int x)
{
    memset(link,-1,sizeof(link));
    for(int i=1;i<=n;i++)
    {
        memset(mark,-1,sizeof(mark));
        if(!dfs(i))
            return false;
    }
    return true;
}
int main()
{
    int tt;
    scanf("%d",&tt);
    while(tt--)
    {
        scanf("%d",&n);
        maxx=0,minn=INF;
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=n;j++)
            {
                scanf("%d",&mp[i][j]);
                minn=min(minn,mp[i][j]);
                maxx=max(maxx,mp[i][j]);
            }
        }
        l,r,mid;
        int ans=0;
        l=0,r=maxx-minn;
        while(l<=r)
        {
            mid=(l+r)>>1;
            bool flag=false;
            for(p=minn;p+mid<=maxx;p++)
            {
                if(check(mid))
                {
                    flag=true;
                    break;
                }
            }
            if(flag)
            {
                ans=mid;
                r=mid-1;
            }
            else
                l=mid+1;
        }
        printf("%d\n",ans);
    }
    return 0;
}