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 ALL(a) (a).begin(), (a).end()
#define ll long long

using namespace std;

signed main(){
	int n; cin >> n;
	vector<int> a(2*n*n-2*n),b(2*n*n-2*n),c(n*n, -1), d(n*n, -1);
	vector<vector<int> > e(n*n);
	for(int i = 0; i < a.size(); i++){
		cin >> a[i] >> b[i];
		a[i]--;
		b[i]--;
		e[a[i]].push_back(b[i]);
		e[b[i]].push_back(a[i]);
	}
	for(int i = 0; i < e.size(); i++){
		if(e[i].size() == 2){
			d[i] = 0;
			queue<pair<int, int> > q;
			q.push(make_pair(i, 0));
			while(!q.empty()){
				auto tmp = q.front();
				q.pop();
				for(auto v : e[tmp.first]){
					if(d[v] == -1){
						d[v] = tmp.second+1;
						assert(0 <= d[v] && d[v] < 2*n);
						q.push(make_pair(v,tmp.second+1));
					}
				}
			}
			break;
		}
	}
	for(int i = 0; i < n*n; i++){
		if(d[i] == n-1 && e[i].size() == 2){
			c[i] = 0;
			queue<pair<int, int> > q;
			q.push(make_pair(i, 0));
			while(!q.empty()){
				auto tmp = q.front();
				q.pop();
				for(auto v : e[tmp.first]){
					if(c[v] == -1){
						c[v] = tmp.second+1;
						assert(0 <= c[v] && c[v] < 2*n);
						q.push(make_pair(v,tmp.second+1));
					}
				}
			}
			break;
		}
	}
	//cerr << "kkk" << endl;
	//vector<vector<int> > m(n, vector<int>(n));
	map<pair<int, int>, int> m;
	for(int i = 0; i < c.size(); i++){
		m[make_pair(d[i], c[i])] = i;
	}
	for(int i = 0; i < n; i++){
		for(int j = 0; j < n; j++){
			int p1 = i+j;
			int p2 = i + n - j - 1;
			cout << m[make_pair(p1, p2)]+1;
			if(j != n-1)cout << " ";
		}
		cout << endl;
	}
	/*
	for(int i = 0; i < d.size(); i++){
		int r = (d[i] - c[i] + n)/2;
		int C = (c[i] + d[i])/2 - 1;
		assert(0 <= r && r < n);
		assert(0 <= C && C < n);
		m[r][C] = i;
	}
	for(int i = 0; i < n; i++){
		cout << (m[i][0]+1);
		for(int j = 1; j < n; j++){
			cout << " " << (m[i][j]+1);
		}
		cout << endl;
	}
	*/

	return 0;
}