【PAT】1020. Tree Traversals (25)

import java.util.ArrayList;import java.util.LinkedList;import java.util.Scanner;class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int val) {this.val = val;left = null;right = null;}}public class Main {public static void preorderPrint(TreeNode root) {if (root != null) {System.out.print(" " + root.val);if (root.left != null)preorderPrint(root.left);if (root.right != null)preorderPrint(root.right);}}public static ArrayList<Integer> levelPrint(TreeNode root) {ArrayList<Integer> resultList = new ArrayList<Integer>();LinkedList<TreeNode> linkedList = new LinkedList<TreeNode>();if (root == null)return null;linkedList.add(root);int preNum = 1, nextNum = 0;while (linkedList.size() > 0) {TreeNode firstNode = linkedList.getFirst();linkedList.removeFirst();resultList.add(firstNode.val);preNum--;if (firstNode.left != null) {linkedList.add(firstNode.left);nextNum++;}if (firstNode.right != null) {linkedList.add(firstNode.right);nextNum++;}if (preNum == 0) {preNum = nextNum;nextNum = 0;}}return resultList;}public static TreeNode createTree(int[] a, int[] b, int af, int al, int bf,int bl) {int i,nextlen;if (al < af)return null;TreeNode root = new TreeNode(a[al]);for (i = bf; i <= bl; i++) {if (a[al] == b[i])break;}nextlen=i-bf;/*System.out.println("af:"+af+" al:"+al+" bf:"+bf+" bl:"+bl);System.out.println("i="+i);*/root.left = createTree(a, b, af, af + nextlen - 1, bf, bf + nextlen - 1);root.right = createTree(a, b, af + nextlen, al - 1, bf + nextlen + 1, bl);return root;}public static void main(String[] args) {// TODO Auto-generated method stubScanner input = new Scanner(System.in);int n = input.nextInt();int[] a = new int[n];// postorderint[] b = new int[n];// inorderfor (int i = 0; i < n; i++) {a[i] = input.nextInt();}for (int i = 0; i < n; i++) {b[i] = input.nextInt();}TreeNode rootNode = null;rootNode = createTree(a, b, 0, n - 1, 0, n - 1);ArrayList<Integer> ansList=levelPrint(rootNode);for(int i=0;i<ansList.size();i++){if(i!=ansList.size()-1)System.out.print(ansList.get(i)+" ");else System.out.println(ansList.get(i));}}}