Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	io := NewIo()
	defer io.Flush()
	N := io.NextInt()
	nodes := make([]Node, N*N+1)
	for i := 0; i < 2*N*N-2*N; i++ {
		a, b := io.NextInt(), io.NextInt()
		nodes[a].adj = append(nodes[a].adj, b)
		nodes[b].adj = append(nodes[b].adj, a)
	}
	ninja(nodes, N, io)
}

type Node struct {
	adj []int
}

func ninja(nodes []Node, N int, io *Io) {
	used := make([]bool, N*N+1)
	m := make([][]int, N)
	fst := 0
	for i := 0; i < N; i++ {
		m[i] = make([]int, N)
		for j := 0; j < N; j++ {
			if len(nodes[i*N+j].adj) == 2 {
				fst = i*N + j
			}
		}
	}
	m[0][0] = fst
	used[fst] = true
	for j := 1; j < N; j++ {
		u := 0
		deg := 3
		if j == N-1 {
			deg = 2
		}
		for _, v := range nodes[m[0][j-1]].adj {
			if !used[v] && len(nodes[v].adj) == deg {
				u = v
			}
		}
		m[0][j] = u
		used[u] = true
	}
	for i := 1; i < N; i++ {
		for j := 0; j < N; j++ {
			u := 0
			for _, v := range nodes[m[i-1][j]].adj {
				if !used[v] {
					u = v
				}
			}
			m[i][j] = u
			used[u] = true
		}
	}
	for _, a := range m {
		io.PrintIntSlice(a)
	}
}

// I/O template
type Io struct {
	reader    *bufio.Reader
	writer    *bufio.Writer
	tokens    []string
	nextToken int
}

func NewIo() *Io {
	return &Io{
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
	}
}

func (io *Io) Flush() {
	err := io.writer.Flush()
	if err != nil {
		panic(err)
	}
}

func (io *Io) NextLine() string {
	var buff []byte
	for {
		line, isPrefix, err := io.reader.ReadLine()
		if err != nil {
			panic(err)
		}
		buff = append(buff, line...)
		if !isPrefix {
			break
		}
	}
	return string(buff)
}

func (io *Io) Next() string {
	for io.nextToken >= len(io.tokens) {
		line := io.NextLine()
		io.tokens = strings.Fields(line)
		io.nextToken = 0
	}
	s := io.tokens[io.nextToken]
	io.nextToken++
	return s
}

func (io *Io) NextInt() int {
	i, err := strconv.Atoi(io.Next())
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) NextFloat() float64 {
	i, err := strconv.ParseFloat(io.Next(), 64)
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) Println(a ...interface{}) {
	fmt.Fprintln(io.writer, a...)
}

func (io *Io) Printf(format string, a ...interface{}) {
	fmt.Fprintf(io.writer, format, a...)
}

func (io *Io) PrintIntSlice(a []int) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func (io *Io) PrintStringSlice(a []string) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func Log(name string, value interface{}) {
	fmt.Fprintf(os.Stderr, "%s=%+v\n", name, value)
}

func ExampleIo() {
	io := NewIo()
	defer io.Flush()
	a := make([]int, 0, 3)
	a[0], a[1], a[2] = io.NextInt(), io.NextInt(), io.NextInt()
	io.Println(a)
	io.PrintIntSlice(a)
	Log("io", a)
}

C++: #include <bits/stdc++.h>
#define rep(i,n) for(int i = 0 ; i < n;++i)
#define pb push_back
using namespace std;
int n;
int a[110][110];
vector<int> G[11000];
int sumi[100020]={0};
int jou[11000];
int main(void){

cin>>n;
for(int i=0;i<2*n*n-2*n;i++){
int u,v;
cin>>u>>v;
G[u].pb(v);
G[v].pb(u);
}
vector<int> ka,hen;
for(int i=0;i<n*n;i++){
	if(G[i].size()==2)ka.pb(i);
	if(G[i].size()==3) hen.pb(i); 
	jou[i]=G[i].size();
}

a[1][1]=ka[0];
sumi[a[1][1]]=1;

//cout<<a[1][1]<<endl;
for(int i=2;i<=n-1;i++){
	int y;
	for(int j=0;j<G[a[1][i-1]].size();j++){
		if(G[G[a[1][i-1]][j]].size()==3  && sumi[G[a[1][i-1]][j]]==0) y=G[a[1][i-1]][j];
	}
	a[1][i]=y;
	sumi[y]=1;

//	cout<<y<<endl;
}
{
	int y;
	for(int j=0;j<G[a[1][n-1]].size();j++){
		if(G[G[a[1][n-1]][j]].size()==2 && sumi[G[a[1][n-1]][j]]==0) y=G[a[1][n-1]][j];
	}
	a[1][n]=y;		
	sumi[y]=1;

//	cout<<y<<endl;
}
for(int i=2;i<n;i++){
	for(int j=0;j<G[a[i-1][1]].size();j++){
		if(G[G[a[i-1][1]][j]].size()==3 && sumi[G[a[i-1][1]][j]]==0){
			a[i][1]=G[a[i-1][1]][j];
			sumi[a[i][1]]=1;
		}
	}	

	for(int k=2;k<=n;k++){
		for(int j=0;j<G[a[i-1][k]].size();j++)for(int l=0;l<G[a[i][k-1]].size();l++){
			if(G[a[i-1][k]][j]==G[a[i][k-1]][l] && sumi[G[a[i][k-1]][l]]==0){
				a[i][k]=G[a[i-1][k]][j];
				sumi[a[i][k]]=1;
			}
		}
	}

}

for(int j=0;j<G[a[n-1][1]].size();j++){
	if(G[G[a[n-1][1]][j]].size()==2 && sumi[G[a[n-1][1]][j]]==0){
		a[n][1]=G[a[n-1][1]][j];
		sumi[G[a[n-1][1]][j]]=1;
	}
}

for(int k=2;k<=n;k++){
		for(int j=0;j<G[a[n-1][k]].size();j++)for(int l=0;l<G[a[n][k-1]].size();l++){
			if(G[a[n-1][k]][j]==G[a[n][k-1]][l] && sumi[G[a[n][k-1]][l]]==0){
				a[n][k]=G[a[n-1][k]][j];
				sumi[a[n][k]]=1;
			}
		}
	}

for(int i=1;i<=n;i++){
	for(int j=1;j<=n;j++){
cout<<a[i][j]<<" ";
}
cout<<endl;
}
	return 0;


}