Go: package main

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

var (
	sc = bufio.NewScanner(os.Stdin)
)

type Color int

const (
	ColorBlack Color = iota
	ColorRed
)

type Node struct {
	ID    int
	X, Y  int
	Color Color
	Nexts []*Node
}

func main() {
	for sc.Scan() {
		if sc.Text() == "0 0" {
			break
		}
		chunks := strings.Split(sc.Text(), " ")
		w, _ := strconv.Atoi(chunks[0])
		h, _ := strconv.Atoi(chunks[1])

		// Initialize map
		m := map[int]map[int]*Node{}
		for x := 1; x <= w; x++ {
			m[x] = map[int]*Node{}
			for y := 1; y <= h; y++ {
				m[x][y] = &Node{ID: x + y*w, X: x, Y: y}
			}
		}
		for x := 1; x <= w; x++ {
			for y := 1; y <= h; y++ {
				nexts := []*Node{}
				if n, ok := m[x-1][y]; ok {
					nexts = append(nexts, n)
				}
				if n, ok := m[x][y-1]; ok {
					nexts = append(nexts, n)
				}
				if n, ok := m[x+1][y]; ok {
					nexts = append(nexts, n)
				}
				if n, ok := m[x][y+1]; ok {
					nexts = append(nexts, n)
				}
				m[x][y].Nexts = nexts
			}
		}

		// Set colors
		queue := []*Node{}
		touchedIDs := map[int]struct{}{}
		for y := 1; y <= h; y++ {
			sc.Scan()
			for i, c := range sc.Text() {
				switch c {
				case '.', '@':
					n := m[i+1][y]
					n.Color = ColorBlack
					if c == '@' {
						queue = append(queue, n)
						touchedIDs[n.ID] = struct{}{}
					}
				case '#':
					m[i+1][y].Color = ColorRed
				}
			}
		}

		// Search
		visitedIDs := map[int]struct{}{}
		for {
			if len(queue) == 0 {
				break
			}
			n := queue[0]
			queue = queue[1:]
			visitedIDs[n.ID] = struct{}{}
			for _, next := range n.Nexts {
				if next.Color == ColorRed {
					continue
				}
				if _, ok := touchedIDs[next.ID]; !ok {
					queue = append(queue, next)
					touchedIDs[n.ID] = struct{}{}
				}
			}
		}
		fmt.Println(len(visitedIDs))
	}
}

Python: x=0
y=0
b=[]
t=[]
dir=[[1,0],[0,1],[-1,0],[0,-1]]
ans=0

def dfs(p_x,p_y):
  global b,t,ans
  if t[p_y][p_x] or not b[p_y][p_x]: return
  ans+=1
  t[p_y][p_x]=True
  for i in dir:
    dfs(p_x+i[0],p_y+i[1])

while True:
  x=0
  y=0
  w,h=map(int,input().split())
  if w==0 and h==0: break
  b=[[False]*(w+2) for i in range(h+2)]
  t=[[False]*(w+2) for i in range(h+2)]
  ans=0
  for i in range(1,h+1):
    tmp=list(input())
    for j in range(1,w+1):
      b[i][j]=(tmp[j-1] in {'.','@'})
      if tmp[j-1]=='@': x=j;y=i
  dfs(x,y)
  print(ans)

Python: from collections import deque

def solve(W, H, field):
    dire = [(1,0), (0,1), (-1,0), (0,-1)]
    for i in range(H):
        for j in range(W):
            if (field[i][j]=="@"):
                s = (i,j)
    check = [[0]*W for i in range(H)]
    q = deque()
    q.append(s)
    check[s[0]][s[1]] = 1
    ret = 1
    while q:
        y, x = q.popleft()
        for dy, dx in dire:
            if (y+dy<H) and (y+dy>=0) and (x+dx<W) and (x+dx>=0):
                if (field[y+dy][x+dx] == ".") and (not check[y+dy][x+dx]):
                    q.append((y+dy, x+dx))
                    check[y+dy][x+dx] = 1
                    ret += 1
    return ret

def main():
    ans = []
    while True:
        W, H = list(map(int, input().split()))
        if (not W) and (not H):
            break
        field = [input() for i in range(H)]
        ans.append(solve(W, H, field))
    for i in ans:
        print(i)
    
main()

Python: #!/usr/bin/env python3
#AOJ B
from collections import deque

def bfs():
    while 1:
        W,H = map(int,input().split())
        if W == 0 and H == 0:
            break
        maze = [list(input()) for _ in range(H)]
        check = [[False for _ in range(W)] for _ in range(H)]
        #print(maze)
        dx = [1,0,-1,0]
        dy = [0,1,0,-1]
        for i in range(H):
            for j in range(W):
                if maze[i][j] == '@':
                    sx,sy = j,i
                    check[i][j] = True

        ans = 1
        que = deque()
        que.append((sx,sy))
        while que:
            x,y = que.pop()
            for i in range(4):
                nx,ny = x + dx[i],y + dy[i]

                if 0 <= nx < W and 0 <= ny < H and maze[ny][nx] == '.' and check[ny][nx] == False:
                    que.append((nx,ny))
                    check[ny][nx] = True
                    ans += 1
        print(ans)
    return

if __name__ == '__main__':
    bfs()

Python: while True:
    w, h = map(int, input().split())
    if h == 0:
        break
    m = [list(input()) for _ in range(h)]
    sx = 0
    sy = 0
    for yi, row in enumerate(m):
        if '@' in row:
            sy = yi
            sx = row.index('@')
    def dfs(x, y):
        if x < 0 or w <= x or y < 0 or h <= y or m[y][x] == '#':
            return 0
        else:
            m[y][x] = '#'
            dy = [1, -1] + [0] * 2
            dx = [0] * 2 + [1, -1]
            return sum([dfs(x+dx[i], y+dy[i]) for i in range(4)]) + 1
    print(dfs(sx, sy))

C++: #include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cassert>
#include <string>
#include <algorithm>
#include <vector>
#include <valarray>
#include <queue>
#include <stack>
#include <functional>
#include <iostream>
#include <iomanip>
#include <map>
#include <set>
#include <list>
#include <limits>
#include <numeric>
#include <utility>
#include <deque>
#include <unordered_set>
#include <unordered_map>
#include <regex>
#include <array>
#include <bitset>
#include <complex>
#include <tuple>
#include <random>

using namespace std;
using ll = long long;
const int INF = 1e9;
const ll MOD = 1e9 + 7;
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

void dfs(int x, int y, int &sum, vector<string> &field)
{
  field[y][x] = '#';
  sum++;
  for (int i = 0; i < 4; ++i)
  {
    int ny = y + dy[i], nx = x + dx[i];
    if (0 <= ny && ny < field.size() && 0 <= nx && nx < field[0].size() && field[ny][nx] == '.')
    {
      dfs(nx, ny, sum, field);
    }
  }
}

int main()
{
  int w, h;
  while (cin >> w >> h, w || h)
  {
    vector<string> field(h);
    for (auto &e : field)
      cin >> e;
    int sx, sy;
    for (int i = 0; i < h; ++i)
    {
      for (int j = 0; j < w; ++j)
      {
        if (field[i][j] == '@')
        {
          sy = i, sx = j;
          field[i][j] = '#';
        }
      }
    }
    int sum = 0;
    dfs(sx, sy, sum, field);
    cout << sum << endl;
  }

  return 0;
}

C++: //red and black
#if 0

#endif // 0
#include<iostream>
#include<queue>
#include<stack>
using namespace std;
#define MAX 1000
const int dx[]={1,0,-1,0}, dy[]={0,-1,0,1};
int matri[MAX][MAX],s[MAX][MAX];
int w,h;
bool valid(int x,int y)
{
    return x>=0&&x<w&&y>=0&&y<h&&matri[x][y];
}
int main()
{
    while(cin>>w>>h&&w&&h)
    {
        pair<int,int> p;
        for(int j=0;j<h;j++)
            for(int i=0;i<w;i++)
            {
                s[i][j]=1;
                char c;
                cin>>c;
                if(c=='.')
                    matri[i][j]=1;
                else if(c=='#')
                {
                    matri[i][j]=0;
                    s[i][j]=0;
                }
                else if(c=='@'){
                    matri[i][j]=1;
                    p.first=i;
                    p.second=j;
                }
            }
        stack<pair<int,int> > q;
        int sum=0;
        q.push(p);
        s[p.first][p.second]=0;
        while(!q.empty())
        {
            p=q.top();
            int i;
            for(i=0;i<4;i++)
            {
                int x=p.first+dx[i];
                int y=p.second+dy[i];
                if(valid(x,y)&&s[x][y])
                {
                    p.first=x;
                    p.second=y;
                    q.push(p);
                    s[x][y]=0;
                    break;
                }
            }
            if(i>=4)
            {
                sum++;
                q.pop();
            }
        }
        cout<<sum<<endl;
    }
    return 0;
}