二维数组的生成-【leetcode118- Pascal's Triangle 】
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一、题目
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]]
二、解法
2.1 渣渣法一
array = [[1 for j in range(i)]for i in range(1,numRows+1)] for i in range(1,numRows): for j in range(i): array[i][j] = array[i-1][j-1] + array[i-1][j] array[i][0] = array[i][-1] = 1 return array2.2 改进法二
class Solution(object): def generate(self, numRows): """ :type numRows: int :rtype: List[List[int]] """ array = [] for i in range(numRows): array.append([1]*(i+1)) for j in range(i): array[i][j] = array[i-1][j-1] + array[i-1][j] array[i][0] = array[i][-1] = 1 return array
三、改进
通过法二第2、4行的改进,使得二维数组的初始化时间减少,由O(n2)变成O(n)
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