0118._pascal's_triangle.md

118. Pascal's Triangle

难度: Easy

刷题内容

原题连接

• https://leetcode.com/problems/pascals-triangle/description/

内容描述

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]
]

解题方案

思路 1 - 时间复杂度: O(N^2)- 空间复杂度: O(N)******

高中数学知识，把行数理理清楚就ok, beats 100%

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

思路 2 - 时间复杂度: O(N^2)- 空间复杂度: O(N)******

或者可以写得更简单一些，这里谢谢荼靡大佬的想法，棒！但是时间真的不好，才 beats 1.02%

class Solution:
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        res = [[1]]
        for i in range(1, numRows):
            res.append(list(map(lambda x,y:x+y, [0]+res[-1], res[-1]+[0])))
        return res[:numRows]