python-leetcode-不同的二叉搜索树 II

95. 不同的二叉搜索树 II - 力扣（LeetCode）

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def generateTrees(self, n: int) -> List[Optional[TreeNode]]:
        if n == 0:
            return []
        return self._generate_trees(1, n)
    
    def _generate_trees(self, start, end):
        trees = []
        # 如果区间为空，则返回 [None] 作为空树的情况
        if start > end:
            trees.append(None)
            return trees
        
        # 枚举每个数字作为根节点
        for i in range(start, end + 1):
            # 递归生成所有可能的左子树和右子树
            left_trees = self._generate_trees(start, i - 1)
            right_trees = self._generate_trees(i + 1, end)
            
            # 将所有左子树和右子树组合起来
            for left in left_trees:
                for right in right_trees:
                    root = TreeNode(i)
                    root.left = left
                    root.right = right
                    trees.append(root)
        
        return trees