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]