118.Pascal's Triangle

Given a non-negative integer numRows, generate the first numRows of Pascal's triangle.

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

Example:

Input: 5
Output:
[
[1],
[1,1],
[1,2,1],
[1,3,3,1],
[1,4,6,4,1]
]

class Solution(object):
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        res = []
        for i in range(numRows):
            res.append([0 for j in range(i+1)])
            for j in range(i+1):
                if j==0 or j==i:
                    res[i][j]=1
                    continue
                res[i][j] = res[i-1][j-1] + res[i-1][j]
        return res