leetcode 【 Pascal's Triangle 】python 实现

题目：

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]
]

代码：oj测试通过 Runtime: 46 ms

 1 class Solution:
 2     # @return a list of lists of integers
 3     def generate(self, numRows):
 4         if numRows < 1:
 5             return []
 6         pascal = []
 7         first_row = [1]
 8         pascal.append(first_row)
 9         for i in range(1,numRows):
10             tmp = []
11             tmp.append(1)
12             for j in range(len(pascal[i-1])):
13                 if j == len(pascal[i-1])-1:
14                     tmp.append(1)
15                 else:
16                     tmp.append(pascal[i-1][j] + pascal[i-1][j+1])
17             pascal.append(tmp)
18         return pascal

思路：

排除几个special case

然后把pascal写成如下的形式，比较容易写代码：

[1]

[1,1]

[1,2,1]

[1,3,3,1]

[1,4,6,4,1]