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 <bits/stdc++.h>
#include <iterator>
using namespace std;

struct Fast {Fast(){std::cin.tie(0);ios::sync_with_stdio(false);}} fast;

/* cpp template {{{ */

/* short */
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define Fi first
#define Se second
#define ALL(v) begin(v), end(v)
#define RALL(v) (v).rbegin(), (v).rend()
#define X real()
#define Y imag()

/* REPmacro */
#define REPS(i, a, n) for (ll i = (a); i < (ll)(n); ++i)
#define rep(i, n) REPS(i, 0, n)
#define REP1(i,n) for (ll i = 1; i <= (ll)(n); ++i)
#define RREP(i, n) REPS(i, 1, n + 1)
#define DEPS(i, a, n) for (ll i = (a); i >= (ll)(n); --i)
#define DEP(i, n) DEPS(i, n, 0)
#define EACH(i, n) for (auto&& i : n)

/* debug */
#define debug(x) cerr << x << " " << "(L:" << __LINE__ << ")" << '\n';

/* alias */
using ll = long long;
using ull = unsigned long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using pii = pair<int, int>;
using D = double;
using P = complex<D>;
using vs = vector<string>;
template <typename T> using PQ = priority_queue<T>;
template <typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;

/* const */
const int INF = 1001001001;
const ll LINF = 1001001001001001001ll;
const int MOD = 1e9 + 7;
const D EPS = 1e-9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1}, dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

/* func */
inline bool inside(int y, int x, int H, int W) {return y >= 0 && x >= 0 && y < H && x < W;}
inline int in() {int x; cin >> x; return x;}
inline ll IN() {ll x; cin >> x; return x;}
inline vs split(const string& t, char c) {vs v; stringstream s(t); string b; while(getline(s, b, c)) v.eb(b); return v;}
template <typename T> inline bool chmin(T& a, const T& b) {if (a > b) a = b; return a > b;}
template <typename T> inline bool chmax(T& a, const T& b) {if (a < b) a = b; return a < b;}
template <typename T, typename S> inline void print(const pair<T, S>& p) {cout << p.first << " " << p.second << endl;}
template <typename T> inline void print(const T& x) {cout << x << '\n';}
template <typename T, typename S> inline void print(const vector<pair<T, S>>& v) {for (auto&& p : v) print(p);}
template <typename T> inline void print(const vector<T>& v, string s = " ") {rep(i, v.size()) cout << v[i] << (i != (ll)v.size() - 1 ? s : "\n");}

int w,h;
vvi field;
void dfs(int y, int x)
{
  field[y][x]=0;
  rep(i,8)
  {
    int nx=x+dx[i], ny=y+dy[i];
    if(nx<w&&0<=nx&&ny<h&&0<=ny&&field[ny][nx]==1)
    {
      dfs(ny,nx);
    }
  }
}

signed main() 
{
  while(cin>>w>>h, w||h)
  {
    field=vvi(100,vi(100,-1));
    int n;
    rep(y,h) rep(x,w)
    {
      cin>>n;
      field[y][x]=n;
    }
    int x,y;
    int cnt=0;
    rep(y,h) rep(x,w)
    {
      if(field[y][x]==1) 
      {
        dfs(y,x);
        cnt++;
      }
    }
    print(cnt);
  }

  return 0;
}

C++: #include <iostream>
using namespace std;

constexpr int MAX_H = 55;
constexpr int MAX_W = 55;

int H, W;
int grid[MAX_H][MAX_W];
bool reached[MAX_H][MAX_W];

constexpr int dh[]{-1, -1, -1, 0, 0, +1, +1, +1};
constexpr int dw[]{-1, 0, +1, -1, +1, -1, 0, +1};

void dfs(int h, int w) {
  reached[h][w] = true;

  for (int i{}; i < 8; ++i) {
    int nh = h + dh[i];
    if (nh < 0 || nh >= H)
      continue;
    int nw = w + dw[i];
    if (nw < 0 || nw >= W)
      continue;
    if (grid[nh][nw] == 0 || reached[nh][nw])
      continue;
    dfs(nh, nw);
  }
}

int main() {
  while (true) {
    cin >> H >> W;
    if (H == 0 && W == 0)
      break;
    for (int h{}; h < H; ++h) {
      for (int w{}; w < W; ++w) {
        reached[h][w] = false;
        cin >> grid[h][w];
      }
    }

    int island{};
    for (int h{}; h < H; ++h) {
      for (int w{}; w < W; ++w) {
        if (grid[h][w] == 0 || reached[h][w])
          continue;
        dfs(h, w);
        ++island;
      }
    }

    cout << island << endl;
  }

  return 0;
}

C++: #include <cstdio>

using namespace std;

int parent[2500];

int Find(int x){
    if(parent[x] != x) parent[x] = Find(parent[x]);
    return parent[x];
}

void Union(int x, int y){
    x = Find(x); y = Find(y);
    parent[x] = y;
}

int main(){
    int n,m;
    int M[50][50];
    
    while(true){
        scanf("%d %d",&m,&n);
        
        if(n == 0) break;
        
        for(int i = 0;i < n;++i)
            for(int j = 0;j < m;++j)
                scanf("%d",&M[i][j]);
        
        for(int i = n*m - 1;i >= 0;--i)
            parent[i] = i;
        
        for(int i = 0;i < n;++i)
            for(int j = 0;j < m;++j)
                if(M[i][j] == 1)
                    for(int dr = -1;dr <= 1;++dr)
                        for(int dc = -1;dc <= 1;++dc)
                            if(i + dr >= 0 && i + dr < n && j + dc >= 0 && j + dc < m && M[i + dr][j + dc] == 1)
                                Union(m * i + j, m * (i + dr) + j + dc);
        
        int ans = 0;
        
        for(int i = 0;i < n;++i)
            for(int j = 0;j < m;++j)
                if(M[i][j] == 1 && Find(m * i + j) == m * i + j)
                    ++ans;
        
        printf("%d\n",ans);
    }
    
    return 0;
}