Go: // AOJ 1160: How Many Islands? http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1160

package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
)

var SEA = 0
var LAND = 1

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

func discoverIslands(M, V [][]int, H, W int) int {
	// 島を探す
	queue := list.New()
	islands := 0
	for i := 1; i <= H; i++ {
		for j := 1; j <= W; j++ {
			// 訪問済みの土地ならスキップ
			if V[i][j] == 1 {
				continue
			}

			// 訪問中の土地が海なら訪問済みにしてスキップ
			if M[i][j] == SEA {
				V[i][j] = 1
				continue
			}

			// 未訪問の陸地が見つかったので
			// 島の数を1つ増やし、この陸地から辿れる陸地を訪問していく
			islands++
			queue.PushBack([]int{i, j})

			for queue.Len() > 0 {
				cur := queue.Remove(queue.Front()).([]int)
				h, w := cur[0], cur[1]
				if V[h][w] == 1 {
					continue
				}
				V[h][w] = 1

				// 全方向に未訪問の陸地がないか探索
				for v := -1; v <= 1; v++ {
					for l := -1; l <= 1; l++ {
						dh := h + v
						dw := w + l
						if M[dh][dw] == LAND && V[dh][dw] == 0 {
							queue.PushBack([]int{dh, dw})
						}
					}
				}
				/*
					if M[h-1][w] == LAND {
						queue.PushBack([]int{h - 1, w})
					}
					if M[h-1][w+1] == LAND {
						queue.PushBack([]int{h - 1, w + 1})
					}
					if M[h][w+1] == LAND {
						queue.PushBack([]int{h, w + 1})
					}
					if M[h+1][w+1] == LAND {
						queue.PushBack([]int{h + 1, w + 1})
					}
					if M[h+1][w] == LAND {
						queue.PushBack([]int{h + 1, w})
					}
					if M[h+1][w-1] == LAND {
						queue.PushBack([]int{h + 1, w - 1})
					}
					if M[h][w-1] == LAND {
						queue.PushBack([]int{h, w - 1})
					}
					if M[h-1][w-1] == LAND {
						queue.PushBack([]int{h - 1, w - 1})
					}
				*/
			}
		}
	}
	return islands
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	for {
		W, H := nextInt(sc), nextInt(sc)

		if W == 0 && H == 0 {
			break
		}
		// Initialize map and visted list
		M := make([][]int, H+2)
		V := make([][]int, H+2)
		for i := 0; i < H+2; i++ {
			M[i] = make([]int, W+2)
			V[i] = make([]int, W+2)
		}
		for i := 1; i <= H; i++ {
			for j := 1; j <= W; j++ {
				M[i][j] = nextInt(sc)
			}
		}

		islands := discoverIslands(M, V, H, W)

		fmt.Println(islands)
	}
}

C++: #include<iostream>
#include<fstream>

using namespace std;

	ifstream fin;
	ofstream fout;

	//http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1160&lang=jp

	int gomi = 0;

	int a[52][52] = {};
	int check(int, int);

	int main(){

		fin.open("input.txt");
		fout.open("output.txt");

		//		int w = 0, h = 0;
		int width = 0, height = 0;
		int count = 0;


		while (1){
			for (int i = 0; i < 50; i++)
				for (int j = 0; j < 50; j++)
					a[i + 1][j + 1] = 0;

			cin >> width >> height;
			if (width == 0 && height == 0)break;

			for (int i = 0; i < height; i++){
				for (int j = 0; j < width; j++){
					//初期化
					gomi = a[i + 1][j + 1] = 0;

					cin >> a[i + 1][j + 1];
				}
			}

			for (int i = 0; i < height; i++){
				for (int j = 0; j < width; j++){
					if (a[i + 1][j + 1] == 1){
						check(i + 1, j + 1);
//						a[i + 1][j + 1] = 1;
						count++;
//						cout << i + 1 << "  " << j + 1 << endl;
					}
				}
			}
//			cout << count << endl;
			fout << count << endl;

			//初期化
			count = 0;
			for (int i = 0; i < height; i++){
				for (int j = 0; j < width; j++){
					a[i + 1][j + 1] = 0;
				}
			}
		}
	}

	int check(int y, int x){
		for (int i = -1; i <= 1; i++){
			for (int j = -1; j <= 1; j++){
				if (a[y + i][x + j] == 1){
					if (i == 0 && j == 0)
						j = 1;
					a[y + i][x + j] = 0;
					check(y + i, x + j);
				}
			}
		}
		return 0;
	}

/*	int check(int y, int x){
		if (a[y + 1][x] == 1){
			a[y + 1][x] = 0;
			check(y + 1, x);
		}
		//-----------------------------
		if (a[y][x + 1] == 1){
			a[y][x + 1] = 0;
			check(y, x + 1);
		}
		//-----------------------------
		if (a[y - 1][x] == 1){
			a[y - 1][x] = 0;
			check(y - 1, x);
		}
		//-----------------------------
		if (a[y][x - 1] == 1){
			a[y][x - 1] = 0;
			check(y, x - 1);
		}
		//-----------------------------
		if (a[y + 1][x + 1] == 1){
			a[y + 1][x + 1] = 0;
			check(y + 1, x + 1);
		}
		//-----------------------------
		if (a[y + 1][x - 1] == 1){
			a[y + 1][x - 1] = 0;
			check(y + 1, x - 1);
		}
		//-----------------------------
		if (a[y - 1][x + 1] == 1){
			a[y - 1][x + 1] = 0;
			check(y - 1, x + 1);
		}
		//-----------------------------
		if (a[y - 1][x - 1] == 1){
			a[y - 1][x - 1] = 0;
			check(y - 1, x - 1);
		}
		//-----------------------------
		return 0;
	}*/

C++: #include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int W, H;
vector<vector<bool>> field;

void dfs(vector<vector<bool>>& visited, int h, int w){
    if(visited[h][w]) return;
    visited[h][w]=true;
    int dx[3]={-1, 0, 1};
    int dy[3]={-1, 0, 1};
    for(int yi=0; yi<3; ++yi){
        for(int xi=0; xi<3; ++xi){
            if(field[h+dy[yi]][w+dx[xi]]) dfs(visited, h+dy[yi], w+dx[xi]);
        }
    }
}

int solve(){
    vector<vector<bool>> visited(H+2, vector<bool>(W+2));
    int ans=0;
    for(int h=1; h<=H; ++h){
        for(int w=1; w<=W; ++w){
            if(!field[h][w]) continue;
            if(visited[h][w]) continue;
            dfs(visited, h, w);
            ++ans;
        }
    }
    return ans;
}

int main(){
    while(true){
        cin >> W >> H;
        if(W==0 && H==0) break;
        field=vector<vector<bool>>(H+2, vector<bool>(W+2));
        for(int h=1; h<=H; ++h){
            for(int w=1; w<=W; ++w){
                char c; cin >> c;
                field[h][w]=c=='1';
            }
        }
        cout << solve() << endl;
    }
    return 0;
}

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

using ll = long long;
using ld = long double;
const int INF = 1e9;
const double EPS = 1e-9;
const ll MOD = 1e9 + 7;

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

void dfs(int y, int x, vector<vector<int>> &c)
{
  c[y][x] = 0;
  for (int i = 0; i < 8; ++i)
  {
    int ny = y + dy[i], nx = x + dx[i];
    if (0 <= nx && nx < c[0].size() && 0 <= ny && ny < c.size() && c[ny][nx])
      dfs(ny, nx, c);
  }
}

int main()
{
  int w, h;
  while (cin >> w >> h, w || h)
  {
    vector<vector<int>> c;
    c.clear();
    c.shrink_to_fit();
    c.assign(h, vector<int>(w));
    for (int i = 0; i < h; ++i)
    {
      for (int j = 0; j < w; ++j)
      {
        cin >> c[i][j];
      }
    }
    int cnt = 0;
    for (int i = 0; i < h; ++i)
    {
      for (int j = 0; j < w; ++j)
      {
        if (c[i][j])
        {
          dfs(i, j, c);
          cnt++;
        }
      }
    }
    cout << cnt << endl;
  }

  return 0;
}