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:
Test Cases
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| class Solution:
def generate(self, numRows: int) -> List[List[int]]:
|
solution_test.py1
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| 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.py1
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| 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
|
