LeetCode 103. 二叉树的锯齿形层序遍历

LeetCode 103. 二叉树的锯齿形层序遍历

题目描述

LeetCode 103. 二叉树的锯齿形层序遍历
提示：

一、解题关键词

    树中节点数目在范围 [0, 2000] 内
    -100 <= Node.val <= 100

二、解题报告

1.思路分析

2.时间复杂度

3.代码示例

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        List<List<Integer>> resultList = new ArrayList<>();
        if(null == root){return resultList;}

        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        boolean leftToRight = true;

        while(!queue.isEmpty()){
            List<Integer> level = new ArrayList<>();
            int count = queue.size();
            for(int i = 0; i < count;i++){
                TreeNode node = queue.poll();
                if(leftToRight){
                    level.add(node.val);
                }else{
                    level.add(0,node.val);
                }
                if(node.left != null){
                    queue.add(node.left);
                }
                if(node.right != null){
                    queue.add(node.right);
                }
            }
            resultList.add(level);
            leftToRight = !leftToRight;
        }
        return resultList;

    }
}

2.知识点

广度优先，深度优先 都可以做 需要给出反转的标识

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总结