leetcode118 Pascal's Triangle

Posted 2020-11-28 yawenw

 1 """
 2 Given a non-negative integer numRows, generate the first numRows of Pascal‘s triangle.
 3 In Pascal‘s triangle, each number is the sum of the two numbers directly above it.
 4 Example:
 5 Input: 5
 6 Output:
 7 [
 8      [1],
 9     [1,1],
10    [1,2,1],
11   [1,3,3,1],
12  [1,4,6,4,1]
13 ]
14 """
15 """
16 解法一：
17 先来一个自己写的AC
18 直来直去，将第一行第二行单独拿出来讨论
19 第三行以后按照规律循环
20 """
21 class Solution1:
22     def generate(self, numRows):
23         if numRows <= 0:
24             return []
25         if numRows == 1:
26             return [[1]]
27         res = [[1], [1, 1]]
28         if numRows == 2:
29             return res
30         queue = [1, 1]
31         while numRows - 2:
32             temp = [1]
33             for i in range(len(queue)-1):
34                 temp.append(queue[i] + queue[i+1])
35             temp.append(1)
36             res.append(temp)
37             queue = temp
38             numRows -= 1
39         return res
40 """
41 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)
42 新的一行前后各添0,再相加即为下一行
43   0 1 3 3 1
44  +1 3 3 1 0
45  =1 4 6 4 1
46 """
47 class Solution:
48     def generate(self, numRows: int) -> List[List[int]]:
49         if numRows == 0:
50             return []
51         res = [[1]]
52         for i in range(1, numRows):
53             res.append(list(map(lambda x, y: x+y, res[-1] + [0], [0] + res[-1])))
54             # map(function, list1, list2)
55             #res[-1]代表当前最后一行,前后添0
56             #  0 1 3 3 1
57             # +1 3 3 1 0
58             # =1 4 6 4 1
59         return res
60         # ‘+‘与extend功能相同,合二为一 []+[]=[]
61         # append是再末尾添加新的对象 [].append([]) = [[]]