Find bottom left tree value

# 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 findBottomLeftValue(self, root: Optional[TreeNode]) -> int:
        maxdepth = 0
        res = root.val
        depth = 0
        def backtrack(node):
            nonlocal maxdepth
            nonlocal depth
            nonlocal res
            if not node.left and not node.right:
                if depth > maxdepth:
                    res = node.val
                    maxdepth = depth

            if node.left:
                depth += 1
                backtrack(node.left)
                depth -= 1

            if node.right:
                depth += 1
                backtrack(node.right)
                depth -= 1

        backtrack(root)

        return res

    # def findBottomLeftValue(self, root: Optional[TreeNode]) -> int:
    #     queue = deque([root])
    #     res = root.val
    #     while queue:
    #         size = len(queue)
    #         for i in range(size):
    #             node = queue.popleft()
    #             if i == 0:
    #                 res = node.val

    #             if node.left:
    #                 queue.append(node.left)
    #             if node.right:
    #                 queue.append(node.right)
    #     return res

Find Bottom Left Tree Value

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Given the root of a binary tree, return the leftmost value in the last row of the tree.

 

Example 1:

Input: root = [2,1,3]
Output: 1

Example 2:

Input: root = [1,2,3,4,null,5,6,null,null,7]
Output: 7

 

Constraints:

• The number of nodes in the tree is in the range [1, 104].
• -231 <= Node.val <= 231 - 1