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

 class Solution:
     # @return a list of lists of integers
     def generate(self, numRows):
         if numRows < 1:
             return []
         pascal = []
         first_row = [1]
         pascal.append(first_row)
         for i in range(1,numRows):
             tmp = []
             tmp.append(1)
             for j in range(len(pascal[i-1])):
                 if j == len(pascal[i-1])-1:
                     tmp.append(1)
                 else:
                     tmp.append(pascal[i-1][j] + pascal[i-1][j+1])
             pascal.append(tmp)
         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]