All Possible Full Binary Trees

Intuition

Solution

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def allPossibleFBT(self, N: int) -> List[TreeNode]:
        if N == 0:
            return []
        elif N == 1:
            return [TreeNode(0)]

        ans = []
        for l in range(1, N - 1):
            r = N - l - 1
            lefts = self.allPossibleFBT(l)
            rights = self.allPossibleFBT(r)
            for left in lefts:
                for right in rights:
                    node = TreeNode(0)
                    node.left, node.right = left, right
                    ans.append(node)
        return ans