leetcode118 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]
]
"""
"""
解法一：
先来一个自己写的AC
直来直去，将第一行第二行单独拿出来讨论
第三行以后按照规律循环
"""
class Solution1:
    def generate(self, numRows):
        if numRows <= 0:
            return []
        if numRows == 1:
            return [[1]]
        res = [[1], [1, 1]]
        if numRows == 2:
            return res
        queue = [1, 1]
        while numRows - 2:
            temp = [1]
            for i in range(len(queue)-1):
                temp.append(queue[i] + queue[i+1])
            temp.append(1)
            res.append(temp)
            queue = temp
            numRows -= 1
        return res
"""
解法二：用map函数(自己知道这个函数,但想不到可以用,这就是和大佬的差距)
新的一行前后各添0,再相加即为下一行
  0 1 3 3 1
 +1 3 3 1 0
 =1 4 6 4 1
"""
class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        if numRows == 0:
            return []
        res = [[1]]
        for i in range(1, numRows):
            res.append(list(map(lambda x, y: x+y, res[-1] + [0], [0] + res[-1])))
            # map(function, list1, list2)
            #res[-1]代表当前最后一行,前后添0
            #  0 1 3 3 1
            # +1 3 3 1 0
            # =1 4 6 4 1
        return res
        # '+'与extend功能相同,合二为一 []+[]=[]
        # append是再末尾添加新的对象 [].append([]) = [[]]