leetcode @python 118. Pascal's Triangle

题目链接

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

题目原文

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,
Return

[
[1],
[1,1],
[1,2,1],
[1,3,3,1],
[1,4,6,4,1]
]

题目大意

给定一个整数，返回一个帕斯卡三角形

解题思路

自上而下构建三角形，特殊处理边缘位置的值

代码

class Solution(object):
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        ans = [0] * numRows
        for i in range(numRows):
            if i == 0:
                ans[i] = [1]
            elif i == 1:
                ans[i] = [1, 1]
            else:
                ans[i] = [0] * (i + 1)
                ans[i][0] = ans[i][i] = 1
                for j in range(1, i):
                    ans[i][j] = ans[i - 1][j - 1] + ans[i - 1][j]
        return ans