You are 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 Explanation: The last row is [1,3], so the leftmost value is 1.
Example 2:
Input: root = [1,2,3,4,null,5,6,null,null,7] Output: 7 Explanation: The last row contains only the node 7.
Constraints:
[1, 104].-231 <= Node.val <= 231 - 1