题目：输入一棵二叉树的根节点，求该树的深度。从根节点到叶子结点一次经过的结点形成树的一条路径，最长路径的长度为树的深度。根节点的深度为1.
最大深度
<pre><code>`
func treeMaxDepth(rootNode:TreeNode?) -> Int {
if rootNode == nil {
return 0
}
let leftDepth:Int = treeMaxDepth(rootNode: rootNode?.leftChild)
let rightDepth:Int = treeMaxDepth(rootNode: rootNode?.rightChild)
return leftDepth > rightDepth ? leftDepth + 1 : rightDepth + 1
}`</code></pre>
最小深度
最小深度： 从根节点开始到叶子节点结束的最短路径上的节点数，递归解决过程:
①空树最小深度是0.
②左子树空： 右子树最小深度+ 1
③右子树空： 左子树最小深度 + 1
④min(左子树最小深度，右子树最小深度) + 1
<pre><code>`
func treeMinDepth(rootNode:TreeNode?) -> Int {
if rootNode == nil {
return 0
}
let leftDepth:Int = treeMinDepth(rootNode: rootNode?.leftChild)
let rightDepth:Int = treeMinDepth(rootNode: rootNode?.rightChild)
if leftDepth == 0 {
return rightDepth + 1
}
if rightDepth == 0 {
return leftDepth + 1
}
return leftDepth < rightDepth ? leftDepth + 1 : rightDepth + 1
}`</code></pre>
测试代码:
<pre><code>`
var util:TreeUtil = TreeUtil()
var depthData:[String] = ["1","2","4","#","#","5","7","#","#","#","3","#","6","#","#"]
var preRootNode:TreeNode?
util.createTreeByPreOrderData(root: &preRootNode, listData: depthData)
var binaryTreePath:BinaryTreePath = BinaryTreePath()
var binaryDepth:Int = binaryTreePath.treeMaxDepth(rootNode: preRootNode)
print("FlyElephant-最大深度--(binaryDepth)")
var binaryMinDepth:Int = binaryTreePath.treeMinDepth(rootNode: preRootNode)
print("FlyElephant-最小深度--(binaryMinDepth)")`</code></pre>
