118. Pascal's Triangle.py

"""
https://leetcode.com/problems/pascals-triangle/

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]]

"""


class Solution(object):
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        result = [[1]]

        for _ in range(1, numRows):
            row = [1]
            prev = result[-1]

            for j in range(1, len(prev)):
                row.append(prev[j] + prev[j - 1])

            row.append(1)
            result.append(row)

        return result