First Value on the Lowest Row

Medium

You are given the root of a non-empty binary tree. Find the lowest level of the tree (the one farthest from the root) and return the value of the leftmost node on it. Note that this node does not have to be a left child: you need the leftmost node of the last level, whatever its parent.

Example 1

root=tree_node([10, 4, 7, None, 2, 9, 1]) → 2

The lowest level is 2, 9, 1. The leftmost of them is 2, even though it is the right child of 4.

Example 2

root=tree_node([5, 3, 8, None, None, 6, None, -4]) → -4

The deepest level holds a single node, -4 (5 → 8 → 6 → -4), so that is the answer.

Example 3

root=tree_node([42]) → 42

Constraints

1 ≤ number of nodes ≤ 10⁴
-2³¹ ≤ Node.val ≤ 2³¹ - 1

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Topics

Tree Depth-First Search Breadth-First Search Binary Tree

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Input

root=tree_node([10, 4, 7, None, 2, 9, 1])

Expected

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