Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	out := make([][]string, 100)
	for i := range out {
		out[i] = make([]string, 100)
	}
	dx := []int{0, 1, 0, -1}
	dy := []int{-1, 0, 1, 0}
	scanner.Scan()
	a, _ := strconv.Atoi(scanner.Text())
	for a > 0 {
		a--
		scanner.Scan()
		b, _ := strconv.Atoi(scanner.Text())
		for i := 0; i < b; i++ {
			for j := 0; j < b; j++ {
				out[i][j] = " "
			}
			out[i][b] = "0"
		}
		if b == 1 {
			fmt.Println("#")
			if a != 0 {
				fmt.Println()
			}
			continue
		}
		if b == 2 {
			fmt.Println("##")
			if a != 0 {
				fmt.Println()
				continue
			}
		}
		row := b -1
		col := 0
		dir := 0
		len := 0
		out[row][col] = "#"
		for {
			nrow := row+dy[dir%4]
			ncol := col+dx[dir%4]
			if dir%4 == 0 && nrow == 0 || dir%4==3&&ncol==0 || dir%4==2&&nrow==b-1 || dir%4==1&&ncol==b-1 {
				row=nrow
				col=ncol
				out[row][col]="#"
				dir++
				len = 1
			} else if out[nrow+dy[dir%4]][ncol+dx[dir%4]]=="#" {
				if len < 3 {
					break
				}
				dir++
				len = 1
			} else {
				row=nrow
				col=ncol
				out[row][col]="#"
				len++
			}
		}
		for i := 0; i < b; i++ {
			for j := 0; j < b; j++ {
				fmt.Printf("%s", out[i][j])
			}
			fmt.Println()
		}
		if a != 0 {
			fmt.Println()
		}
	}
}

C++: #include "bits/stdc++.h"
using namespace std;

//#define int long long
#define DBG 0
#define dump(o) if(DBG){cerr<<#o<<" "<<(o)<<" ";}
#define dumpl(o) if(DBG){cerr<<#o<<" "<<(o)<<endl;}
#define dumpc(o) if(DBG){cerr<<#o; for(auto &e:(o))cerr<<" "<<e;cerr<<endl;}
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(c) begin(c),end(c)
const int INF = sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9 + 7);
template<class T> bool chmax(T &a, const T &b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, const T &b) { if (a > b) { a = b; return true; } return false; }
int N;
bool inrange(int i, int j) { return 0 <= i&&i < N && 0 <= j&&j < N; }

signed main() {
	int d; cin >> d;
	int a[120][120] = {};
	int di[] = { -1,0,1,0 };
	int dj[] = { 0,1,0,-1 };
	rep(h, 0, d) {
		if (h != 0)cout << endl;
		memset(a, 0, sizeof(a));
		cin >> N;

		if (N == 1) { cout << "#" << endl; continue; }
		if (N == 2) { cout << "##" << endl << "# " << endl; continue; }

		int ci = N - 1, cj = 0;
		int dir = 0;
		int cnt = 1;
		while (true) {
			a[ci][cj] = cnt;
			int ni = ci + di[dir], nj = cj + dj[dir];
			if (!inrange(ni, nj)) {
				dir = (dir + 1) % 4;
				ni = ci + di[dir], nj = cj + dj[dir];
			}
			else if (inrange(ni + di[dir], nj + dj[dir]) && a[ni + di[dir]][nj + dj[dir]] != 0) {
				dir = (dir + 1) % 4;
				ni = ci + di[dir], nj = cj + dj[dir];
			}
			dump(ci)dumpl(cj);
			dump(ni + dj[dir])dumpl(nj + dj[dir]);
			if (inrange(ni + di[dir], nj + dj[dir]) && (a[ni + di[dir]][nj + dj[dir]] != 0 || a[ni + di[(dir + 1) % 4]][nj + dj[(dir + 1) % 4]] != 0)) {
				break;
			}
			ci += di[dir];
			cj += dj[dir];

		}
		rep(i, 0, N) {
			rep(j, 0, N) {
				cout << (a[i][j] ? '#' : ' ');
			}
			cout << endl;
		}
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <algorithm>
#include <cassert>
#include <vector>
#include <string>
#include <cmath>
#include <map> 
#include <sstream>
#include <cstdio>
#include <complex>
#include <cstring>
using namespace std;
 
const int MAX= 10000100;

#define loop(i,a,b) for(int i = a ; i < b ; i ++)
#define rep(i,a) loop(i,0,a)
#define all(a) (a).begin(),(a).end()
#define ll long long int
#define gcd(a,b) __gcd(a,b)
#define pb(a) push_back(a)
int GCD(int a, int b) {if(!b) return a; return gcd(b, a%b);}
int lcm(int a, int b) {return a*b / gcd(a, b);}

char maze[110][110];
int dx[] = {0,1,0,-1} , dy[] = {-1,0,1,0};
int size;

bool over(int x,int y){
  return x < 0 || size <= x || y < 0 || size <= y;
}
bool space(int x,int y){
  int cnt = 0;
  rep(i,4){
    int nx = x + dx[i], ny = y + dy[i];
    if(maze[ny][nx] == '#')
      cnt ++;
  }
  return cnt > 1;
}
void dfs(int x,int y,int d){
  if(size <= x) 
    dfs(x-1,y,2);
  if(y < 0)
    dfs(x,y+1,1);
  if(size <= y)
    dfs(x,y-1,3);
  if(space(x,y))
    return ;
  if(over(x,y))return;
  maze[y][x] = '#';
  
  int nnx = x + 2 * dx[d] , nny = y + 2 * dy[d];
  if(maze[nny][nnx] == '#')
    d = (d+1)%4;
  dfs(x+dx[d],y+dy[d],d);

}

void solve(int n){
  size = n;
  dfs(0,n-1,0);
  rep(i,n){
    rep(j,n){
      cout<<maze[i][j];
    }
    cout<<endl;
  }
  cout<<endl;
}

int main(void){
  int n,in;
  cin>>n;
  while(n--){
    cin>>in;
    rep(i,in)rep(j,in)maze[i][j] = '.';
    solve(in);
  }
}

C++: #define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include <stdio.h>
#include <ctype.h>
#include <string>
#include <iostream>
#include <vector>
#include <stack>
#include <fstream>
#include <sstream>
#include <queue>
#include <exception>
#include <cmath>
#include <numeric>
#include <map>
#include <algorithm>
#include <bitset>
#include <set>
#include <functional>

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

using namespace std;
typedef long long int lint;
typedef vector< vector < char > > Mat;

int dx[4] = {0, 1, 0, -1};
int dy[4] = {-1, 0, 1, 0};

void AOJ0141(bool newline)
{
	int n;
	cin >> n;

	if (newline) cout << endl;

	if (n == 1) {
		cout << "#" << endl;
		return;
	}
	if (n == 2) {
		cout << "##" << endl;
		cout << "# " << endl;
		return;
	}

	vector<int> steps;

	steps.push_back(n - 1);
	for (int i = n - 1; i > 0; i -= 2) {
		steps.push_back(i);
		steps.push_back(i);
	}
	if (n % 2 == 0) {
		steps.pop_back();
	}

	Mat spiral(n);
	REP(i, n) spiral[i] = vector<char>(n, ' ');
	int x = 0;
	int y = n - 1;

	spiral[y][x] = '#';

	REP(i, steps.size()) {
		REP(s, steps[i]) {
			x += dx[i % 4];
			y += dy[i % 4];
			spiral[y][x] = '#';
		}
	}

	REP(i, n) {
		REP(j, n) {
			cout << spiral[i][j];
		}
		cout << endl;
	}

	return;
}

int main()
{
	int d;
	cin >> d;

	bool newline = false;
	REP(i, d) {
		AOJ0141(newline);
		newline = true;
	}

	return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstring>
#include <climits>
using namespace std;
static const double EPS = 1e-5;
typedef long long ll;

int sp[101][101];

main(){
	int d;
	cin>>d;
	while(d--){
		int n;
		cin>>n;
		if(n==1){
			cout<<"#"<<endl;
			continue;
		}
		memset(sp,0,sizeof(sp));
		
		int y=n-1,x=0,d=0;
		int c=0;
		while(true){
			
			
			if(d==0){
				if(sp[y-1][x+1]==1)break;
				int cy=y;
				while(cy>=1){
					if(cy>=2 && sp[cy-2][x]==1)break;
					--cy;
				}
				if(y==cy)break;
				d=(d+1)%4;
				for(;cy<=y;y--)sp[y][x]=1;
				++y;
				continue;
			}
			
			if(d==1){
				if(sp[y+1][x+1]==1)break;
				int cx=x;
				while(cx<=n-2){
					if(cx<=n-3 && sp[y][cx+2]==1)break;
					++cx;
				}
				if(x==cx)break;
				d=(d+1)%4;
				for(;cx>=x;x++)sp[y][x]=1;
				--x;
				continue;
			}
			
			if(d==2){
				if(sp[y+1][x-1]==1)break;
				int cy=y;;
				while(cy<=n-2 && !(cy<=n-3 && sp[cy+2][x]==1))++cy;
				if(cy==y)break;
				d=(d+1)%4;
				for(;cy>=y;y++)sp[y][x]=1;
				--y;
				continue;
			}
			
			if(d==3){
				if(sp[y-1][x-1]==1)break;
				int cx=x;
				while(cx>=1 && !(cx>=2 && sp[y][cx-2]==1))--cx;
				if(x==cx)break;
				d=(d+1)%4;
				for(;cx<=x;x--)sp[y][x]=1;
				++x;
				continue;
			}
		}
		for(int i=0;i<n;i++){
			for(int j=0;j<n;j++){
				if(sp[i][j])printf("#");
				else printf(" ");
			}
			puts("");
		}
		if(d!=0)puts("");
	}
}