【PAT】1043. Is It a Binary Search Tree (25)

import java.util.ArrayList;import java.util.Arrays;import java.util.Scanner;class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int val) {this.val = val;left = null;right = null;}}/** * BST，a节点左边的节点value都【小于】a，右边的节点【大于等于】a * a先序数组，b中序数组 * 在BST（中序从小到大）中，当存在有重复元素的时候，在中序中应该第一个出现a[0]的位置 * 而在BST镜像树中（中序从大到小），在中序中应该最后一个出现a[0]的位置 *  * 故：在createTree和createTree1中，遍历b的顺序不同 * for (i = bf; i <= bl; i++) 和for (i = bl; i >= bf; i--)区别 * * 创建日期：2014年10月10日 * @author chenshanfu */public class Main {private static ArrayList<Integer> resultList = new ArrayList<Integer>();public static void postorderPrint(TreeNode root) {if (root != null) {if (root.left != null)postorderPrint(root.left);if (root.right != null)postorderPrint(root.right);resultList.add(root.val);}}// 从小到大public static boolean check(int[] a, int[] b, int af, int al, int bf, int bl) {int i, nextlen;if (al < af)return true;for (i = bf; i <= bl; i++) {if (b[i] == a[af]) {break;}}nextlen = i - bf;for (int j = af + 1; j <= al; j++) {if ((j <= af + nextlen && a[j] >= b[i])|| (j >= af + nextlen + 1 && a[j] < b[i])) {/* * System.err.println("i="+i); System.err.println("j="+j); */return false;}}return check(a, b, af + 1, af + nextlen, bf, bf + nextlen - 1)&& check(a, b, af + nextlen + 1, al, bf + nextlen + 1, bl);}// 从大到小public static boolean check1(int[] a, int[] b, int af, int al, int bf,int bl) {int i, nextlen;if (al < af)return true;for (i = bl; i >= bf; i--) {if (b[i] == a[af]) {break;}}nextlen = i - bf;for (int j = af + 1; j <= al; j++) {if ((j <= af + nextlen && a[j] < b[i])|| (j >= af + nextlen + 1 && a[j] >= b[i])) {return false;}}return check1(a, b, af + 1, af + nextlen, bf, bf + nextlen - 1)&& check1(a, b, af + nextlen + 1, al, bf + nextlen + 1, bl);}//从小到大创建树/** *  * * @param a先序 * @param b中序 * @param af先序开始位置（包含） * @param al先序结束位置（包含） * @param bf中序开始位置（包含） * @param bl中序结束位置（包含） * @return * 创建日期：2014年10月10日 * 修改说明： * @author chenshanfu */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[af]);for (i = bf; i <= bl; i++) {if (b[i] == a[af]) {break;}}nextlen = i - bf;root.left = createTree(a, b, af + 1, af + nextlen, bf, bf + nextlen - 1);root.right = createTree(a, b, af + nextlen + 1, al, bf + nextlen + 1,bl);return root;}//从大到小创建树public static TreeNode createTree1(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[af]);for (i = bl; i >= bf; i--) {if (b[i] == a[af]) {break;}}nextlen = i - bf;root.left = createTree(a, b, af + 1, af + nextlen, bf, bf + nextlen - 1);root.right = createTree(a, b, af + nextlen + 1, al, 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];// preorderint[] b = new int[n];// inorder 从小到大int[] c = new int[n];// inorder 从大到小for (int i = 0; i < n; i++) {a[i] = input.nextInt();}for (int i = 0; i < n; i++) {b[i] = a[i];}Arrays.sort(b);for (int i = 0; i < n; i++) {c[i] = b[n - 1 - i];}/*System.err.println(check(a, b, 0, n - 1, 0, n - 1));System.err.println(check1(a, c, 0, n - 1, 0, n - 1));*/if (check(a, b, 0, n - 1, 0, n - 1)) {TreeNode rootNode = null;rootNode = createTree(a, b, 0, n - 1, 0, n - 1);postorderPrint(rootNode);System.out.println("YES");for (int i = 0; i < resultList.size(); i++) {if (i != resultList.size() - 1)System.out.print(resultList.get(i) + " ");elseSystem.out.println(resultList.get(i));}} else if (check1(a, c, 0, n - 1, 0, n - 1)) {TreeNode rootNode = null;rootNode = createTree1(a, c, 0, n - 1, 0, n - 1);postorderPrint(rootNode);System.out.println("YES");for (int i = 0; i < resultList.size(); i++) {if (i != resultList.size() - 1)System.out.print(resultList.get(i) + " ");elseSystem.out.println(resultList.get(i));}} else {System.out.println("NO");}}}