Pascal’s Triangle

1. Pascal’s Triangle

Difficulty: Easy

Related Topics: Array, Dynamic Programming

Given an integer numRows, return the first numRows of Pascal’s triangle.

In Pascal’s triangle, each number is the sum of the two numbers directly above it as shown:

Example 1:

Input: numRows = 5 Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

Example 2:

Input: numRows = 1 Output: [[1]]

Code:

class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        pascal = [[] for i in range(numRows)]
        for index in range(len(pascal)):
            if index == 0:
                pascal[index] = [1]
            elif index == 1:
                pascal[index] = [1,1]
            else:
                for i in range(len(pascal[index-1])):
                    if i != len(pascal[index-1])-1:
                        pascal[index].append(pascal[index-1][i]+pascal[index-1][i+1])
                pascal[index].append(1)
                pascal[index].insert(0,1)
        return pascal

Feedbacks:

I first set the base case when there are one and two rows. And then I used dynamic programming algorithms to calculate the elements of rows which is over 2. It passed the problem, but I think I can make the code more simpler.