題目:
給一個binary,找一個最短的深度,最短路徑為根結點到最近的leaf節點,leaf為node with no children。
Given a binary tree, find its minimum depth.
給定一個binary tree,去determine是否高度平衡 兩個subtrees的高度相差沒有超過1
Given a binary tree, determine if it is height-balanced.