剑指Offer-按之字形顺序打印二叉树

package Tree;import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;/*** 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。* 思路：* 先按层次输出二叉树* 判断奇数层和偶数层* 反转arrayList*/
public class Solution9 {public static void main(String[] args) {int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9};Solution9 Solution9 = new Solution9();TreeNode treeNode = Solution9.createBinaryTreeByArray(array, 0);for (ArrayList list :Solution9.Print(treeNode)) {System.out.println(list);}}/*** 之字形打印二叉树* 用reserve反转，时间复杂度高** @param pRoot* @return*/public ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {//arrayLists存储结果ArrayList<ArrayList<Integer>> arrayLists = new ArrayList<>();if (pRoot == null) {return arrayLists;}ArrayList<Integer> arrayList = new ArrayList<>();//使用队列，先进先出Queue<TreeNode> queue = new LinkedList<>();queue.add(pRoot);int start = 0;int end = 1;boolean leftToRight = true;while (!queue.isEmpty()) {TreeNode temp = queue.remove();//添加到本行的arrayListarrayList.add(temp.val);start++;//每打印一个节点，就把此节点的下一层的左右节点加入队列，并记录下一层要打印的个数if (temp.left != null) {queue.add(temp.left);}if (temp.right != null) {queue.add(temp.right);}if (start == end) {start = 0;end = queue.size();if (leftToRight) {arrayLists.add(arrayList);} else {arrayLists.add(reverse(arrayList));}leftToRight = !leftToRight;arrayList = new ArrayList<>();}}return arrayLists;}/*** 反转** @param arrayList* @return*/private ArrayList<Integer> reverse(ArrayList<Integer> arrayList) {ArrayList<Integer> arrayList1 = new ArrayList<>();for (int i = arrayList.size() - 1; i >= 0; i--) {arrayList1.add(arrayList.remove(i));}return arrayList1;}public class TreeNode {int val = 0;TreeNode left = null;TreeNode right = null;public TreeNode(int val) {this.val = val;}}/*** 数据转二叉树** @param array* @param index* @return*/private TreeNode createBinaryTreeByArray(int[] array, int index) {TreeNode tn = null;if (index < array.length) {int value = array[index];tn = new TreeNode(value);tn.left = createBinaryTreeByArray(array, 2 * index + 1);tn.right = createBinaryTreeByArray(array, 2 * index + 2);return tn;}return tn;}
}