题解 | #按之字形顺序打印二叉树#

本题与求二叉树层序遍历类似，只需要在该解法上判断当前遍历的层数，并在相应层次进行反转即可

import java.util.*;
/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        if(pRoot == null){
            return new ArrayList<>();
        }
        Queue<TreeNode> q = new LinkedList<>();
        ArrayList<ArrayList<Integer>> result = new ArrayList<>();
        q.offer(pRoot);
        int level = 0;
        while(!q.isEmpty()){
            int len = q.size();
            ArrayList<Integer> list = new ArrayList<>();
            for(int i = 0;i<len;i++){
                TreeNode temp = q.poll();
                list.add(temp.val);
                if(temp.left != null){
                    q.offer(temp.left);
                }
                if(temp.right != null){
                    q.offer(temp.right);
                }
            }
            if(level % 2 == 1){
                Collections.reverse(list);
            }
            level++;
            result.add(list);
        }
        return result;
    }

}