119. Pascal‘s Triangle II

Easy难度的题目，其实是二项式展开，不需要递归就可以了

Given an integer rowIndex, return the rowIndexth (0-indexed) row of the Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:

Example 1:

Input: rowIndex = 3
Output: [1,3,3,1]

Example 2:

Input: rowIndex = 0
Output: [1]

Example 3:

Input: rowIndex = 1
Output: [1,1]

Constraints:

• 0 <= rowIndex <= 33

  class Solution:
      def fraction(self, n):
          product = 1
          if n==0:
              return 1
          else:
              for i in range(n):
                  product = product*(i+1)
              return product
      def Pr(self, n, m):
          return self.fraction(n)/(self.fraction(m)*self.fraction(n-m))
      def getRow(self, rowIndex):
          output = []
          for i in range(rowIndex+1):
              output.append(int(self.Pr(rowIndex,i)))
          return output