118. Pascal’s Triangle

Problem

Given an integer numRows, return the first numRows of Pascal’s triangle.

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

https://leetcode.cn/problems/pascals-triangle/

Example 1:

Input: numRows = 5
Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

Example 2:

Input: numRows = 1
Output: [[1]]

Constraints:

1 <= numRows <= 30

Test Cases

    python
    
  
class Solution:
    def generate(self, numRows: int) -> List[List[int]]:

solution_test.py下载完整源码

    py
    
  
import pytest

from solution import Solution


@pytest.mark.parametrize('numRows, expected', [
    (5, [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]),
    (1, [[1]]),
])
@pytest.mark.parametrize('sol', [Solution()])
def test_solution(sol, numRows, expected):
    assert sol.generate(numRows) == expected

Thoughts

直接用 119. Pascal’s Triangle II 中组合数的递推方式计算整个杨辉三角即可。

Code

solution.py下载完整源码

    py
    
  
class Solution:
    def generate(self, numRows: int) -> list[list[int]]:
        res = [[1]]
        for n in range(1, numRows):
            row = [1] * (n + 1)
            for m in range(1, n // 2 + 1):
                row[m] = row[n - m] = row[m - 1] * (n - m + 1) // m
            res.append(row)

        return res

#Problem

#Test Cases

#Thoughts

#Code

Problem

Test Cases

Thoughts

Code