118. Pascal's Triangle

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

Python

Recursive

class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        if numRows == 1:
            return [[1]]
        if numRows == 2:
            return [[1], [1, 1]]

        return self._generate(3, numRows, [[1], [1, 1]])

    def _generate(self, level, targetLevel, result):
        if level > targetLevel:
            return result

        pre_level = result[-1]
        current = [1]
        for i in range(1, len(pre_level)):
            pre = pre_level[i-1]
            cur = pre_level[i]
            current.append(pre+cur)
        current.append(1)
        result.append(current)

        return self._generate(level+1, targetLevel, result)