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<pair<int, int>> directions = {
    {1,0}, {0,1}, {-1,0}, {0,-1}, {1,1}, {1,-1}, {-1,1}, {-1,-1}
};
void dfs(Graph &chart, int x, int y) {
    int H = chart.size(), W = chart[0].size();
    chart[x][y] = -1;
    for (int i = 0; i < directions.size(); i++) {
        int nx = x + directions[i].first;
        int ny = y + directions[i].second;
        if (nx < 0 || nx >= H || ny < 0 || ny >= W) continue;
        if (chart[nx][ny] == 1) dfs(chart, nx, ny);
    }
}

int main() {
    while (true) {
        int H, W;
        cin >> W >> H;
        if (H == 0 && W == 0) break;
        Graph chart(H, vector<int>(W));
        for (int i = 0; i < H; i++) for (int j = 0; j < W; j++) {
            cin >> chart[i][j];
        }
        int cnt = 0;
        for (int i = 0; i < H; i++) for (int j = 0; j < W; j++) {
            if (chart[i][j] == 1) {
                dfs(chart, i, j);
                cnt++;
            }
        }
        cout << cnt << endl;
    }
    return 0;
}

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

int w,h;
int c[50][50];
vector<vector<int> > visited;
int dx[]={1,1,0,-1,-1,-1,0,1};
int dy[]={0,-1,-1,-1,0,1,1,1};

bool dfs(int x,int y){
    if(visited[x][y]) return false;
    visited[x][y]=1;

    for(int d=0;d<8;d++){
        int i=x+dx[d];
        int j=y+dy[d];
        if(0<=i&&i<h&&0<=j&&j<w){
            if(c[i][j]){
                dfs(i,j);
            }  
        }
    }
    return true;
}

int solve(int w,int h){

    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]){
                cnt+=dfs(i,j);
            }
        }
    }
    cout<<cnt<<endl;
}

int main(){
    visited.assign(50,vector<int>(50,0));
    while(1){
        cin>>w>>h;
        if(!(w))break;

        solve(w,h);
    }
    
    return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

int c[64][64];

void paint(int y, int x) {
  if (y < 0 || y >= 50 || x < 0 || x >= 50) return;
  if (c[y][x] == 0) return;
  c[y][x] = 0;
  for (int dy = -1; dy <= 1; ++dy) {
    for (int dx = -1; dx <= 1; ++dx) {
      paint(y + dy, x + dx);
    }
  }
}

int main() {
  int H, W;
  while (cin >> W >> H, H) {
    for (int i = 0; i < H; ++i) {
      for (int j = 0; j < W; ++j) {
        cin >> c[i][j];
      }
    }
    int res = 0;
    for (int y = 0; y < H; ++y) {
      for (int x = 0; x < W; ++x) {
        if (c[y][x] == 1) {
          ++res;
          paint(y, x);
        }
      }
    }
    cout << res << endl;
  }
  return 0;
}

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

using namespace std;

int w, h;
int field[51][51];
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

void dfs(int x, int y)
{
    field[y][x] = -1;

    for (int i = 0; i < 4; i++)
    {
        int nx = x + dx[i];
        int ny = y + dy[i];

        if (nx < 0 || ny < 0 || nx >= w || ny >= h)
            continue;

        if (field[ny][nx] == 1)
            dfs(nx, ny);
    }
}

int main()
{
    while (cin >> w >> h, w || h)
    {
        for (int y = 0; y < h; y++)
        {
            for (int x = 0; x < w; x++)
            {
                cin >> field[y][x];
            }
        }

        int ans = 0;

        for (int y = 0; y < h; y++)
        {
            for (int x = 0; x < w; x++)
            {
                if (field[y][x] == 1)
                {
                    dfs(x, y);
                    ans++;
                }
            }
        }

        cout << ans << endl;
    }

    return 0;
}

C++: #include "bits/stdc++.h"
#include<unordered_map>
#include<unordered_set>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
template<class T>
using Table = vector<vector<T>>;

//
int dx8[8] = { -1,-1,-1, 0, 1, 1, 1, 0 };
int dy8[8] = { -1, 0, 1, 1, 1, 0,-1,-1 };
//6:28
vector<vector<int>>as;
void check(int y, int x) {
	for (int i = 0; i < 8; ++i) {
		int nx = x + dx8[i];
		int ny = y + dy8[i];
		if (as[ny][nx]) {
			as[ny][nx] = 0;
			check(ny, nx);
		}
	}
}
int main() {
	while (1) {
		as.clear();
		int w, h; cin >> w >> h;
		if (!w)break;
		as.resize(h+2);
		for (int i = 0; i <= h+1; ++i) {
			as[i].emplace_back(0);
			if (i != 0 && i != h + 1) {
				for (int j = 0; j < w; ++j) {
					int c; cin >> c;
					as[i ].emplace_back(c);
				}
			}
			else {
				for (int j = 0; j < w; ++j) {
					as[i].emplace_back(0);
				}
			}
			
			as[i].emplace_back(0);
		}
		int ans = 0;
		for (int i = 1; i <= h; ++i) {
			for (int j = 1; j <= w; ++j) {
				if (as[i][j]) {
					ans++;
					check(i, j);
				}
			}
		}
		cout << ans << endl;
	}
	return 0;
}