Pascal's Triangle

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> res;
        vector<int> lastRow;
        lastRow.push_back(1);
        res.push_back(lastRow);
        if (!numRows) {
            return {};
        } 
        
        for (int i = 1; i < numRows; i++) {
            vector<int> newRow;
            for (int j = 0; j < lastRow.size() + 1; j++) {
                if (j == 0 || j == lastRow.size()) {
                    newRow.push_back(1);
                    continue;
                }
                newRow.push_back(lastRow[j-1] + lastRow[j]);
            }
            res.push_back(newRow);
            lastRow = newRow;
        }
        return res;
    }
};