Runtime: 192 ms, faster than 98.20% of C# online submissions for Pascal's Triangle II.
Memory Usage: 26.3 MB, less than 26.80% of C# online submissions for Pascal's Triangle II.

public class Solution {
    public IList<int> GetRow(int rowIndex) {
        
        
        var result = new List<int>() {1};
        List<int> prevList = null;
        int currIdx = 1;
        
        while(currIdx <= rowIndex){
            prevList = result;
            result = new List<int>();
            result.Add(1);
            for (int colIdx=1; colIdx < currIdx; colIdx++){
                result.Add(prevList[colIdx]+ prevList[colIdx-1]);
            }
            // Add last one
            result.Add(1);
            currIdx++;
        }
        return result;
    }
}