119.pascals-triangle-ii

Statement

简体中文English

Metadata

• Link: 杨辉三角 II
• Difficulty: Easy
• Tag: 数组 动态规划

给定一个非负索引 rowIndex，返回「杨辉三角」的第 rowIndex 行。

在「杨辉三角」中，每个数是它左上方和右上方的数的和。

 

示例 1:

输入: rowIndex = 3
输出: [1,3,3,1]

示例 2:

输入: rowIndex = 0
输出: [1]

示例 3:

输入: rowIndex = 1
输出: [1,1]

 

提示:

• 0 <= rowIndex <= 33

 

进阶：

你可以优化你的算法到 O(rowIndex) 空间复杂度吗？

Metadata

• Link: Pascal's Triangle II
• Difficulty: Easy
• Tag: Array Dynamic Programming

Given an integer rowIndex, return the rowIndexth (0-indexed) row of the Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:

 

Example 1:

Input: rowIndex = 3
Output: [1,3,3,1]

Example 2:

Input: rowIndex = 0
Output: [1]

Example 3:

Input: rowIndex = 1
Output: [1,1]

 

Constraints:

• 0 <= rowIndex <= 33

 

Follow up: Could you optimize your algorithm to use only O(rowIndex) extra space?

Solution

Python 3

from typing import List


class Solution:
    def getRow(self, rowIndex: int) -> List[int]:
        res = [[1]]
        pre = res[0]
        for _ in range(rowIndex):
            cur_res = [1]

            for i in range(len(pre) - 1):
                cur_res.append(pre[i] + pre[i + 1])

            cur_res.append(1)
            res.append(cur_res)
            pre = cur_res
        return res[-1]

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最后更新: October 11, 2023