Build the first numRows rows of Pascal's triangle.
Example 1
Input: numRows = 5
Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]
Explanation: Each element is the sum of the two elements above it.
Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]
Explanation: Each element is the sum of the two elements above it.
Example 2
Input: numRows = 1
Output: [[1]]
Explanation: The first row of Pascal's triangle is always [1].
Output: [[1]]
Explanation: The first row of Pascal's triangle is always [1].