技術標籤：演算法

還行，自己現在寫出來了，速度也還行，這題主要是廣度遍歷模板掌握好就行

package Group4;

import Group3.Test2;

import java.util.*;

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}
public class Test6 {
    public static void main(String[] args) {
        TreeNode treeNode1=new TreeNode(3);
        TreeNode treeNode2=new TreeNode(9);
        TreeNode treeNode3=new TreeNode(20);
        TreeNode treeNode4=new TreeNode(15);
        TreeNode treeNode5=new TreeNode(7);
        treeNode1.left=treeNode2;
        treeNode1.right=treeNode3;
        treeNode3.left=treeNode4;
        treeNode3.right=treeNode5;
        Test6 test6=new Test6();
        List<List<Integer>> lists = test6.zigzagLevelOrder(treeNode1);
        for (int i = 0; i < lists.size(); i++) {
            System.out.println(lists.get(i).toString());
        }
    }
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        List<List<Integer>> res=new ArrayList<>();
        Queue<TreeNode> queue=new ArrayDeque<>();
        if (root==null) return res;
        queue.add(root);
        int temp=queue.size();
        //廣度遍歷
        while (queue.size()!=0)
        {
            List<Integer> list=new ArrayList<>();
            for (int i = 0; i <temp; i++) {
                TreeNode poll = queue.poll();
                list.add(poll.val);
                if (poll.left!=null)
                    queue.add(poll.left);
                if (poll.right!=null)
                    queue.add(poll.right);
            }
            temp=queue.size();
            res.add(list);
        }
        //翻轉
        for (int i = 0; i < res.size(); i++) {
            if (i%2==0)
            {
                continue;
            }else {
                List<Integer> list = res.get(i);
                int left=0;
                int right=list.size()-1;
                while (left<right)
                {
                    int temp1=list.get(left);
                    list.set(left,list.get(right));
                    list.set(right,temp1);
                    left++;
                    right--;
                }
                res.set(i,list);
            }
        }
        return res;
    }
}