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>
using namespace std;
using Graph = vector<vector<int>>;

vector<int> dx = {-1, -1, -1, 0, 1, 1, 1, 0};
vector<int> dy = {-1, 0, 1, 1, 1, 0, -1, -1}; 
int w, h;
int seen[55][55];

void dfs(const Graph &G, int x, int y){
    seen[y][x] = 1;
    for(int i = 0; i < 8; i++){
        if(x + dx[i] < 0 || x + dx[i] >= w || y + dy[i] < 0 || y + dy[i] >= h || G[y + dy[i]][x + dx[i]] == 0) continue;
        if(seen[y + dy[i]][x + dx[i]] == 1) continue;
        dfs(G, x + dx[i], y + dy[i]);
    }
}

int main(){
    while(true){
        cin >> w >> h;
        if(w == 0 && h == 0) break;
        Graph G(h);
        for(int i = 0; i < h; i++){
            for(int j = 0; j < w; j++){
                int k; cin >> k;
                G[i].push_back(k);
            }
        }
        for(int i = 0; i < 55; i++){
          for(int j = 0; j < 55; j++){
            seen[i][j] = 0;
          }
        }
        int cnt = 0; 
        for(int l = 0; l < h; l++){
            for(int m = 0; m < w; m++){
                if(G[l][m] == 1 && seen[l][m] == 0){
                    dfs(G, m, l);
                    cnt++;
                }
            }
        }
        cout << cnt << endl;
    }
}

C++: #include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
using namespace std;

struct UnionFind {
        int n;
        vector<int> parent;
        vector<int> rank;
        vector<int> num;
        int find(int x) {
                if (parent[x] == x) return  x;
                return parent[x] = find(parent[x]);
        }
        UnionFind(int n_) {
                n = n_;
                parent.resize(n);
                for (int i = 0; i < n; i ++) parent[i] = i;
                rank.assign(n, 0);
                num.assign(n, 1);
        }
        void unite(int x, int y) {
                if ((x = find(x)) != (y = find(y))) {
                        if (rank[x] < rank[y]) {
                                parent[x] = y;
                                num[y] += num[x];
                        } else {
                                parent[y] = x;
                                if (rank[x] == rank[y]) rank[x] ++;
                                num[x] += num[y];
                        }
                        n --;
                }
        }
        bool same(int x, int y) { return find(x) == find(y); }
        int get() { return n; }
        int get(int x) { return num[find(x)]; }
};

int main() {
        int w, h;
        while (scanf("%d%d", &w, &h), w) {
                vector<vector<int>> s(h, vector<int> (w));
                int lands = 0;
                map<pair<int, int>, int> ptol;
                for (int i = 0; i < h; i ++) {
                        for (int j = 0; j < w; j ++){
                                scanf("%d", &s[i][j]);
                                if (s[i][j]) {
                                        ptol[make_pair(i, j)] = lands;
                                        lands ++;
                                }
                        }
                }
                UnionFind uf(lands);
                for (int i = 0; i < h; i ++) {
                        for (int j = 0; j < w; j ++) {
                                if (s[i][j]) {
                                        if (i - 1 >= 0 && j + 1 < w && s[i - 1][j + 1]) uf.unite(ptol[make_pair(i, j)], ptol[make_pair(i - 1, j + 1)]);
                                        if (j + 1 < w && s[i][j + 1]) uf.unite(ptol[make_pair(i, j)], ptol[make_pair(i, j + 1)]);
                                        if (i + 1 < h && j + 1 < w && s[i + 1][j + 1]) uf.unite(ptol[make_pair(i, j)], ptol[make_pair(i + 1, j + 1)]);
                                        if (i + 1 < h && s[i + 1][j]) uf.unite(ptol[make_pair(i, j)], ptol[make_pair(i + 1, j)]);
                                }
                        }
                }
                printf("%d\n", uf.get());
        }
        return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll=long long;
typedef pair<int,int> P;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
int w,h;
int nx,ny;
void dfs(vector<vector<int>> &G,int a,int b){
    G.at(a).at(b)=0;
    
    for(int k=-1;k<=1;k++){
        for(int s=-1;s<=1;l++){
            nx=a+k;
            ny=b+s;
        if(0<=nx&& nx<h && 0<=ny&& ny<w && G.at(nx).at(ny)==1) dfs(G,nx,ny);
        }
    }
    return ;
}



int main(){
    int w,h;
    cin>>w>>h;
    vector<vector<int>>G(h,vector<int>(w));
    for(int i=0;i<h;i++){
        for(int j=0;j<w;j++){
            cin>>G.at(i).at(j);
        }
    }
    int count=0;
    for(int i=0;i<h;i++){
        for(int j=0;j<w;j++){
            if(G.at(i).at(j)==1){
                dfs(G,i,j);
                count++;
            }
        }
    }
cout<<count<<endl;
}