LeetCode(Python版)——118. Pascal's Triangle

Given a non-negative integer numRows, generate the first numRows of Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it.

Example:

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

class Solution(object):
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        if numRows == 0:
            return []
        if numRows == 1:
            return [[1]]
        if numRows == 2:
            return [[1], [1, 1]]
        
        triangle = [[1], [1, 1]]
        
        for i in range(3, numRows + 1):
            pre = triangle[i - 2]
            current = [1]
            for j in range(i - 2):
                current.append(pre[j] + pre[j + 1])
            current.append(1)
            triangle.append(current)
        return triangle