118.pascals-triangle

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]
]

class Solution(object):
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        ans = [[1] * n for n in xrange(1, numRows + 1)]
        for i in range(1, numRows + 1):
            for j in range(0, i - 2):
                ans[i - 1][1 + j] = ans[i - 2][j] + ans[i - 2][j + 1]
        return ans