0513-find-bottom-left-tree-value.py

# 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
# Iterative
class Solution:
    def findBottomLeftValue(self, root: Optional[TreeNode]) -> int:

        res = []
        q = deque()
        q.append(root)
        while q:
            qlen = len(q)
            level = []
            for i in range(qlen):
                node = q.popleft()
                if node:
                    q.append(node.left)
                    q.append(node.right)
                    level.append(node.val)
            if level:
                res.append(level)
        return res[-1][0]
      
# recursive
class Solution:
    def findBottomLeftValue(self, root: Optional[TreeNode]) -> int:
        max_height = -1
        res = -1
        def dfs(root, depth):
            nonlocal max_height, res
            if not root:
                return
            if depth > max_height:
                max_height = max(depth, max_height)
                res = root.val
            dfs(root.left, depth + 1)
            dfs(root.right, depth + 1)
        
        dfs(root, 0)
        return res