LeetCode "Game of Life"

class Solution {
public:
// encoding: 2 - 1 to 0; -1 - 0 to live
void gameOfLife(vector<vector<int>>& board) {
int h = board.size();
int w = board[0].size();

//  Pass 1
for(int y = 0; y < h; y ++)
for(int x = 0; x < w; x ++)
{
int cnt = 0;
for(int dx = -1; dx < 2; dx ++)
for(int dy = -1; dy < 2; dy ++)
{
int xx = x + dx, yy = y + dy;
if (xx >=0 && xx < w && yy >= 0 && yy < h && !(xx==x && yy == y))
{
cnt += board[yy][xx] > 0;
}
}

if(board[y][x])
{
if (!(cnt == 2 || cnt == 3))
{
board[y][x] = 2;
}
}
else
{
if(cnt == 3)    board[y][x] = -1;
}
}

//  Pass 2
for(int y = 0; y < h; y ++)
for(int x = 0; x < w; x ++)
{
if (board[y][x] == 2) board[y][x] = 0;
else if (board[y][x] == -1) board[y][x] = 1;
}

}
};