118 Pascal's Triangle

🔀 Pick One

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:

    1
   1 1
  1 2 1
 1 3 3 1
1 4 6 4 1

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
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13

class Solution:
    def __init__(self):
        self.rows = [[1]]
        for i in range(29):
            prev_now = self.rows[-1]
            new_row = [prev_now[0]]
            for i in range(1, len(prev_now)):
                new_row.append(prev_now[i-1] + prev_now[i])
            new_row.append(prev_now[-1])
            self.rows.append(new_row)
    
    def generate(self, numRows: int) -> List[List[int]]:
        return self.rows[:numRows]