B - Highways

https://vjudge.net/contest/348411#problem/B
POJ - 2485

//Kruskal
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<vector>
#include<algorithm>
#define rep(i,x,y) if ((x)<=(y)) for (register int i=(x);i<=(y);i++)
using namespace std;
struct node{
	int a,b,data;
};
int pre[100000];

int find(int a)
{
	if (pre[a]==a)
	  return a;
	else
	  return pre[a]=find(pre[a]);
}

void uni(int a,int b)
{
	a=find(a);
	b=find(b);
	if (a!=b)
	  pre[a]=b;
}
	
bool cmp(node x,node y)
{
	if (x.data<y.data)
	  return true;
	return false;
}

int main()
{
	int t,n,x,tot=0;
	cin>>t;
	while (t--)
	{
		vector <node> a;
		tot=0;
		a.clear();
		cin>>n;
		rep(i,1,n)
		  pre[i]=i;
		rep(i,1,n)
		  rep(j,1,n)
		  {
		  	scanf("%d",&x);
		  	node temp;
		  	if (i<j)
		  	{
		  		temp.a=i;
		  		temp.b=j;
		  		temp.data=x;
		  		a.push_back(temp);
		  	}
		  }
		sort(a.begin(),a.end(),cmp);
		rep(i,0,a.size()-1)
		{
			if (find(a[i].a)!=find(a[i].b))
			{
				uni(a[i].a,a[i].b);
				tot++;
				if (tot==n-1)
				{
				  cout<<a[i].data<<endl;
				  break;
			    }
			}
		}
	}
	return 0;
}