[Solved] 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.

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Question

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:

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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

Python Solution

class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        l=[[1],[1,1],[1,2,1]]
        if numRows<=3:
            return l[:numRows]
        else:
            for i in range(3,numRows):
                a=[1]
                if i%2==0:
                    for j in range(i//2):
                        a.append(l[-1][j] + l[-1][j+1])
                    l.append(a+a[::-1][1:])
                else:
                    for j in range((i//2)+1):
                        a.append(l[-1][j] + l[-1][j+1])
                    l.append(a+a[::-1][2:])

            return l

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