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题目描述
请实现一个函数按照之字形顺序打印二叉树,即第一行按照从左到右的顺序打印,第二层按照从右到左的顺序打印,第三行再按照从左到右的顺序打印,其他行以此类推。例如:
给定二叉树: [3,9,20,null,null,15,7],3
/
9 20 / 15 7 返回其层次遍历结果:[
[3], [20,9], [15,7] ]提示:
节点总数 <= 1000
来源:力扣(LeetCode)
链接:https://leetcode-cn.com/problems/cong-shang-dao-xia-da-yin-er-cha-shu-iii-lcof 著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。JAVA
双栈/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */class Solution { public List
> levelOrder(TreeNode root) { List
> res=new ArrayList<>(); if (root==null) return res; Stack stack1=new Stack<>(); //奇数栈 Stack stack2=new Stack<>(); //偶数栈 int count=1; stack1.push(root); while(!stack1.isEmpty() || !stack2.isEmpty()){ if(count %2==1){ List temp1=new ArrayList<>(); while(!stack1.isEmpty()){ TreeNode top1=stack1.pop(); temp1.add(top1.val); if(top1.left!=null) stack2.push(top1.left); if(top1.right!=null) stack2.push(top1.right); } res.add(temp1); }else{ List temp2=new ArrayList<>(); while (!stack2.isEmpty()){ TreeNode top2=stack2.pop(); temp2.add(top2.val); if(top2.right!=null) stack1.push(top2.right); if(top2.left!=null ) stack1.push(top2.left); } res.add(temp2); } count++; } return res; }}