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] ]bfs+递归 思路基本同 Binary Tree Level Order Traversal
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { List<List<Integer>> res = new ArrayList<>(); public List<List<Integer>> zigzagLevelOrder(TreeNode root) { if (root == null) return res; List<TreeNode> list = new ArrayList<TreeNode>(); list.add(root); levelOrder(list, true); return res; } private void levelOrder(List<TreeNode> list, boolean boo) { if (list.size() == 0) return; List<TreeNode> tn = new ArrayList<TreeNode>(); List<Integer> it = new ArrayList<>(); for (int i = 0; i < list.size(); i++) { TreeNode treeNode = list.get(i); if(boo){ it.add(list.get(i).val); }else{ it.add(list.get(list.size()-i-1).val); } if (treeNode.left != null) { tn.add(list.get(i).left); } if (treeNode.right != null) { tn.add(list.get(i).right); } } res.add(it); levelOrder(tn, !boo); } }
[LeetCode]Binary Tree Zigzag Level Order Traversal
原文地址:http://blog.csdn.net/guorudi/article/details/41454329