leetcode-118 - Pascal's Triangle

動機

水題

Problem

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

Example 2:

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

Constraints:

• 1 <= numRows <= 30

Sol

class Solution:
    def generate(self, n: int) -> List[List[int]]:
        if n == 1:
            return [[1]]
        else:
            ret = self.generate(n-1)
            ret += [[ret[-1][0]] + [ret[-1][i] + ret[-1][i+1] for i in range(len(ret[-1])-1)] + [ret[-1][-1]]]
            return ret