[Leetcode 173] Binary Search Tree Iterator

https://leetcode.com/problems/binary-search-tree-iterator/description/?envType=study-plan-v2&envId=top-interview-150

1) 코드

# 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 BSTIterator:

    def __init__(self, root: Optional[TreeNode]):
        self.arr = []
        self.pos = 0 

        def dfs(node):
            if not node:
                return 
            
            dfs(node.left)
            self.arr.append(node.val)
            dfs(node.right)

        dfs(root)
        return None

    def next(self) -> int:
        num = self.arr[self.pos]
        self.pos += 1 
        return num

    def hasNext(self) -> bool:
        if len(self.arr) == self.pos:
            return False
        return True

2) 해설

• Inorder를 통해 배열을 만들어준 다음에,
  해당 배열을 기준으로 next와 hasNext에 대한 답을 리턴한다.