JZ-059 - Print binary tree in zigzag order

Print binary tree in zigzag order

Topic description

Please implement a function to print the binary tree in a zigzag pattern, that is, the first line is printed in left-to-right order, the second layer is printed in right-to-left order, the third line is printed in left-to-right order, and the other lines are printed in order from left to right. And so on.

title link : print binary tree in zigzag order

code

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;

/**
 * 标题：按之字形顺序打印二叉树
 * 题目描述
 * 请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。
 * 题目链接：
 * https://www.nowcoder.com/practice/91b69814117f4e8097390d107d2efbe0?tpId=13&&tqId=11212&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking
 */
public class Jz59 {

    public ArrayList<ArrayList<Integer>> print(TreeNode pRoot) {
        Queue<TreeNode> treeNodes = new LinkedList<>();
        ArrayList<ArrayList<Integer>> result = new ArrayList<>();
        treeNodes.add(pRoot);
        boolean flag = true; // 当flag为true时，栈从左向右放；当flag为false时，栈从右向左放
        while (!treeNodes.isEmpty()) {
            int cnt = treeNodes.size();
            ArrayList<Integer> curList = new ArrayList<>();
            Stack<TreeNode> curNodes = new Stack<>();
            while (cnt-- > 0) {

                TreeNode t = treeNodes.poll();
                if (t == null) {
                    continue;
                }
                curList.add(t.val);
                if (flag) {
                    curNodes.add(t.left);
                    curNodes.add(t.right);
                } else {
                    curNodes.add(t.right);
                    curNodes.add(t.left);
                }
            }
            flag = !flag;
            while (!curNodes.isEmpty()) {
                treeNodes.add(curNodes.pop());
            }
            if (!curList.isEmpty()) {
                result.add(curList);
            }
        }
        return result;
    }

    public static void main(String[] args) {

    }
}

[Daily Message] As long as you work harder today, the person who can shine like a star in the future is you!