0111. Minimum Depth of Binary Tree

https://leetcode.com/problems/minimum-depth-of-binary-tree

Description

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

Note: A leaf is a node with no children.

Example 1:

**Input:** root = [3,9,20,null,null,15,7]
**Output:** 2

Example 2:

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

Constraints:

• The number of nodes in the tree is in the range [0, 105].

• -1000 <= Node.val <= 1000

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