My solution:

class Solution {
    vector<pair<int, int>> points{ {-1, -1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 1}, {1, -1}, {1, 0}, {1, 1} };
public:
    void gameOfLife(vector<vector<int>>& board) {
        vector<vector<int>> copy = board;
        for (int i = 0; i < copy.size(); i++)
        {
            for (int j = 0; j < copy[0].size(); j++)
            {
                int count = 0;
                for (auto p : points)
                {
                    int x = i + p.first,
                        y = j + p.second;
                    if (x < 0 || x >= copy.size() || y < 0 || y >= copy[0].size())
                        continue;
                    count += copy[x][y];
                }
                if (copy[i][j])
                {
                    if (count < 2) board[i][j] = 0;
                    else if (count > 3) board[i][j] = 0;
                }
                else
                {
                    if (count == 3) board[i][j] = 1;
                }
            }
        }
    }
};