How Many Islands?

How Many Islands?
パソコン甲子園に同じような問題が出題されていたような...

#include<iostream>
using namespace std;
#define rep(i, n) for ( int i = 0; i < n; i++ )
#define MAX 50

int W, H, G[MAX][MAX];

void dfs( int i, int j){
    G[i][j] = 0;
    static const int di[8] = {0, -1, -1, -1, 0, 1, 1, 1};
    static const int dj[8] = {1, 1, 0, -1, -1, -1, 0, 1};
    rep(r, 8){
        int ni = i + di[r];
        int nj = j + dj[r];
        if ( ni < 0 || nj < 0 || ni >= H || nj >= W ) continue;
        if ( G[ni][nj] ) dfs(ni, nj);
    }
}

main(){
    while( cin >> W >> H && W && H ){
        rep(i, H) rep(j, W) cin >> G[i][j];
        int cnt = 0;
        rep(i, H) rep(j, W) if ( G[i][j] ){ cnt++; dfs(i, j); }
        cout << cnt << endl;
    }
}