Pascal's Triangle

题目描述

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]
]

解题方法

这一题和triangle类似，每一层元素是它上面两个元素的和

Solution

class Solution(object):
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        if numRows == 0:
            return []

        result = [[1]]
        if numRows == 1:
            return result
        cur = [1]

        for i in range(1, numRows):
            tmp = [0 for i in range(i+1)]
            for j in range(i+1):
                if j == 0:
                    tmp[0] = 1
                elif j == i:
                    tmp[j] = 1
                else:
                    tmp[j] = cur[j-1] + cur[j]
            result.append(tmp)
            cur = list(tmp)

        return result

Reference