159-118. 杨辉三角

给定一个非负整数 numRows，生成杨辉三角的前 numRows 行(第一个我写的,我越优化,效率越低,懵逼)
class Solution(object):
    def generate1(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        temp_list = [1 for _ in range(numRows)]
        ret_list = []

        for i in range(0, numRows):
            if i < 2:
                ret_list.append(temp_list[:i+1])
                continue
            pre_value = 1
            for j in range(1, i):
                cur_value = temp_list[j]
                temp_value = pre_value + cur_value
                pre_value = cur_value
                temp_list[j] = temp_value

            ret_list.append(temp_list[:i+1])
        return ret_list

    def generate2(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        angleArr = []
        for index in range(0, numRows):
            arr = []
            for j in range(index + 1):
                if j == 0 or j == index:
                    arr.append(1)
                else:
                    newItem = angleArr[index - 1][j - 1] + angleArr[index - 1][j]
                    arr.append(newItem)
            angleArr.append(arr)
        return angleArr

    def generate(self, numRows):
            """
            :type numRows: int
            :rtype: List[List[int]]
            """
            result = []
            for i in range(numRows):
                now = [1]*(i+1)
                if i >= 2:
                    for n in range(1,i):
                        now[n] = pre[n-1]+pre[n]
                result += [now]
                pre = now
            return result


if __name__ == '__main__':
    s1 = Solution()
    n = 7
    root = s1.generate(n)
    print(root)