Binary Tree Zigzag Level Order Traversal

最新推荐文章于 2024-01-19 11:15:23 发布

转载最新推荐文章于 2024-01-19 11:15:23 发布 · 43 阅读

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原文链接：http://www.cnblogs.com/krunning/p/3538829.html

本文详细介绍了如何通过层次遍历的方式，实现二叉树的Z字形层次遍历，并通过实例展示了具体操作过程。

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},

return its zigzag level order traversal as:

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

 1 public class Solution {
 2         public ArrayList<ArrayList<Integer>> zigzagLevelOrder(TreeNode root) {
 3             ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
 4             if(root==null) return res;
 5             LinkedList<TreeNode> cur = new LinkedList<TreeNode>();
 6             cur.offer(root);
 7             int level = 0;
 8             while(!cur.isEmpty()){
 9                 LinkedList<TreeNode> next = new LinkedList<TreeNode>();
10                 ArrayList<Integer> output = new ArrayList<Integer>();
11                 for(TreeNode n:cur){
12                     output.add(n.val);
13                     if(n.left!=null){
14                         next.offer(n.left);
15                     }
16                     if(n.right!=null){
17                         next.offer(n.right);
18                     }
19                 }
20                 if(level%2==1){
21                      Collections.reverse(output);
22                 }
23                 res.add(output);
24                 cur = next;
25                 level++;
26             }
27             return res;
28         }
29     }