题目:根据二叉树的先序遍历结果构建二叉树.

树.jpg

创建二叉树
<pre><code>` func createTreeByPreOrder(root:inout TreeNode?,listData:[String]) {

    rootIndex = rootIndex + 1
    
    if rootIndex >= listData.count {
        return
    }
    
    let data:String = listData[rootIndex] as String
    
    if data == "#" {
        root = nil
    } else {
        root = TreeNode()
        root?.data = data
        createTreeByPreOrder(root: &root!.leftChild, listData: listData)
        createTreeByPreOrder(root: &root!.rightChild, listData: listData)
    }
    
}`</code></pre>

层次遍历二叉树
<pre><code>` func treeLevelOrder(root:TreeNode?) {

    if root == nil {
        return
    }
    
    var arr:[TreeNode] = []
    arr.append(root!)
    
    while arr.count > 0 {
        
        let firstNode:TreeNode = arr[0]
        
        if firstNode.data != nil {
            print("\(firstNode.data!)\t", terminator: "")
            arr.removeFirst()
        }
        
        
        if firstNode.leftChild != nil {
            arr.append(firstNode.leftChild!)
        }
        
        
        if firstNode.rightChild != nil {
            arr.append(firstNode.rightChild!)
        }

    }
    
    print("")
}`</code></pre>

测试代码:
<pre><code>`var tree:Tree = Tree()
var preListData:[String] = ["1","2","4","#","#","5","7","#","#","#","3","#","6","#","#"]
var preOrderRoot:TreeNode?

tree.createTreeByPreOrder(root: &preOrderRoot, listData: preListData)
tree.treeLevelOrder(root: preOrderRoot)
print("FlyElephant")`</code></pre>

FlyElephant.png