Is Find Bottom Left Tree Value easy or hard?

The problem is rated Medium because it requires understanding how traversal order affects which node is discovered first at each depth. Candidates comfortable with BFS level-order traversal or DFS depth tracking usually solve it quickly.

Find Bottom Left Tree Value Python/Java solution

Python and Java solutions typically implement either a queue-based BFS or a recursive DFS. BFS uses a queue to iterate through each level and capture the first node value, while DFS recursively explores left children first and updates the deepest node value encountered.

How to solve Find Bottom Left Tree Value in O(n)?

Traverse the tree once using BFS or DFS. In BFS, process nodes level by level and record the first node of each level. In DFS, track the current depth and update the answer whenever a node is visited at a depth greater than any previously seen depth while exploring left children first. Both strategies visit each node once, giving O(n) time complexity.

What is the best approach for Find Bottom Left Tree Value?

Breadth-First Search (level-order traversal) is typically the most straightforward approach. By processing nodes level by level, the first node encountered at each level is the leftmost node. The value recorded at the final level becomes the answer. This solution runs in O(n) time and O(w) space, where w is the maximum width of the tree.

Is Find Bottom Left Tree Value asked at Google/Amazon/Meta?

Tree traversal problems like this frequently appear in interviews at companies such as Amazon, Google, and Meta. Variations often involve identifying nodes at specific depths, leftmost or rightmost values, or performing level-order traversal on binary trees.

What data structure is used in Find Bottom Left Tree Value?

The main data structures used are queues and recursion. BFS uses a queue to process nodes level by level, while DFS relies on recursion (or an explicit stack) to traverse the tree while tracking depth information.

What is the time complexity of Find Bottom Left Tree Value?

Both BFS and DFS solutions run in O(n) time because every node in the binary tree is visited exactly once. BFS uses O(w) space for the queue where w is the tree's maximum width, while DFS uses O(h) space due to the recursion stack where h is the tree height.

Description Solution Video 7:01

513. Find Bottom Left Tree Value

Medium72.2% acceptance7 companies

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

Asked at 7 companies

Gopuff Josh Technology Microsoft Bloomberg

Google Amazon Meta

Topics

7:01

Still stuck?Read 3 approaches, or watch a walkthrough.

Open solution

LanguageLoading editor…

1# Definition for a binary tree node.
2# class TreeNode:
3#     def __init__(self, val=0, left=None, right=None):
4#         self.val = val
5#         self.left = left
6#         self.right = right
7class Solution:
8    def findBottomLeftValue(self, root: Optional[TreeNode]) -> int:
9        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

[2,1,3]

Input

[1,2,3,4,null,5,6,null,null,7]

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