"Leetcode-Interview algorithm classic-java implementation" "103-binary tree Zigzag level Order traversal (binary hierarchical Z-zigzag traversal)"

"103-binary tree Zigzag level Order traversal (binary tree layered zigzag traversal)" "leetcode-Interview algorithm classic-java Implementation" "All topics Directory Index" Original Question

Given a binary tree, return the zigzag level order traversal of its nodes ' values. (ie, from left-to-right, then right-to-left for the next level and alternate between).
For example:
Given binary Tree {3,9,20,#,#,15,7} ,

    3     9  20    /     15   7

Return its zigzag level order traversal as:

[  [3],  [20,9],  [15,7]]

Main Topic

Given a binary tree, from top to bottom, Z-level traversal, that is: if this layer is left-to-right, the lower is from right to left.

Thinking of solving problems

The binary tree layered traversal is improved using two stacks.

Code Implementation

Tree Node class

publicclass TreeNode {    int val;    TreeNode left;    TreeNode right;    TreeNode(int x) {        val = x;    }}

Algorithm implementation class

ImportJava.Util.Deque;ImportJava.Util.LinkedList;ImportJava.Util.List;/** * Author: Wang Junshu * date:2015-06-23 * time:13:24 * declaration:all rights Reserved!!! */ PublicClass Solution { Public List<List<Integer>>Zigzaglevelorder (TreeNode root) {List<List<Integer>>Result= NewLinkedList<>();if(Root== NULL) {returnResult }//Traversal flag, 0 for left to right, 1 for right-to-leftint flag= 0; TreeNode node;//Record the elements of each layer        List<Integer>Lay= NewLinkedList<>();//bidirectional queue, used as a stack to record the current layer to be processed nodeDeque<TreeNode> Stack = NewLinkedList<>();//Record the next layer of pending nodes.Deque<TreeNode>Nextstack= NewLinkedList<>();Stack.Add (root); while(!Stack.IsEmpty ()) {//delete top of stack elementNode= Stack.Removelast ();//Results QueuedLay.Add (node.Val);//If you are currently traversing from left to right, add in the order of the Zuozi right subtree            if(Flag== 0) {if(node.Left!= NULL) {Nextstack.AddLast (node.left); }if(node.Right!= NULL) {Nextstack.AddLast (node.right); }            }//If you are currently traversing right-to-left, add in the order of the left subtree of the right child tree            Else{if(node.Right!= NULL) {Nextstack.AddLast (node.right); }if(node.Left!= NULL) {Nextstack.AddLast (node.left); }            }//The current layer has been processed            if(Stack.IsEmpty ()) {Deque<TreeNode>Temp=nextstack; Nextstack= Stack;Stack =Temp//mark the direction of the next layer of processingFlag= 1 -Flag//Save the results of this layerResult.Add (lay);//Create a new list to process the results of the next layerLay= NewLinkedList<>(); }        }returnResult }}

Evaluation Results

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leetcode-Interview Algorithm classic-java implementation "" 103-binary tree Zigzag level Order traversal (binary tree layered z-zigzag traversal)