111.minimum depth of binary tree(E)

Posted 2021-01-17 guxuanqing

111. minimum depth of binary tree

 

111. minimum depth of binary tree
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:

Given binary tree [3,9,20,null,null,15,7],

    3
   /   9  20
    /     15   7
return its minimum depth = 2.