二叉搜索树迭代器

173. 二叉搜索树迭代器
分别结合 栈 和 队列 两种数据结构实现。

class BSTIterator:
    """
    结合栈
    173. 二叉搜索树迭代器
    https://leetcode.cn/problems/binary-search-tree-iterator/description/?show=1
    """

    def __init__(self, root: Optional[TreeNode]):
        self.stk = []
        self.pushleftBranch(root)

    # 左侧树枝一撸到底
    def pushleftBranch(self, p):
        while p:
            self.stk.append(p)
            p = p.left

    def next(self) -> int:
        p = self.stk.pop()
        self.pushleftBranch(p.right)
        return p.val

    def hasNext(self) -> bool:
        return len(self.stk) > 0

    def peek(self) -> bool:
        return self.stk[-1].val


class BSTIterator1:
    """
    结合队列
    173. 二叉搜索树迭代器
    https://leetcode.cn/problems/binary-search-tree-iterator/description/?show=1
    """
    def __init__(self, root: Optional[TreeNode]):
        self.deque = collections.deque()
        self.inOrder(root)

    def inOrder(self, root):
        """
        二叉树中序遍历
        :param root:
        :return:
        """
        if not root:
            return
        self.inOrder(root.left)
        self.deque.append(root.value)
        self.inOrder(root.right)

    def next(self) -> int:
        val = self.deque.popleft()
        return val

    def hasNext(self) -> bool:
        return len(self.deque) > 0

    def peek(self) -> bool:
        return self.deque[0]

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BST迭代器应用

1305. 两棵二叉搜索树中的所有元素

# 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:
	"""
	1305. 两棵二叉搜索树中的所有元素
	"""
    def getAllElements(self, root1: TreeNode, root2: TreeNode) -> List[int]:
        t1 = BSTIterator(root1)
        t2 = BSTIterator(root2)

        res = []
        
        while t1.hasNext() and t2.hasNext():
            if t1.peek() > t2.peek():
                res.append(t2.next())
            else:
                res.append(t1.next())

        while t1.hasNext():
            res.append(t1.next())
        
        while t2.hasNext():
            res.append(t2.next())
        
        return res



class BSTIterator:
    """
    结合队列
    173. 二叉搜索树迭代器
    https://leetcode.cn/problems/binary-search-tree-iterator/description/?show=1
    """
    def __init__(self, root: Optional[TreeNode]):
        self.deque = collections.deque()
        self.inOrder(root)

    def inOrder(self, root):
        """
        二叉树中序遍历
        :param root:
        :return:
        """
        if not root:
            return
        self.inOrder(root.left)
        self.deque.append(root.val)
        self.inOrder(root.right)

    def next(self) -> int:
        val = self.deque.popleft()
        return val

    def hasNext(self) -> bool:
        return len(self.deque) > 0

    def peek(self) -> bool:
        return self.deque[0]
        
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