面试题 24: 二叉搜索树的后序遍历序列

一. 题目

输入一个整数数组,判断该数组是不是某二叉搜索树的后序遍历的结果.如果是则返回true,否则返回false.假设输入的数组的任意两个数字都互不相同.

代码请到我的代码库中下载 Point2Offer

二. 代码

package week_5;/**难度系数:*** * 剑指offer: 二叉搜索树的后序遍历序列 * 方法: 熟悉二叉搜索树的概念,左子树所有结点小于根节点,右子树所有结点都大于根节点,左右子树仍是二叉搜索树,键值都不相等 * 测试用例: * @author dingding * Date:2017-7-11 21:40 * Declaration: All Rights Reserved! */public class No24 {    public static void main(String[] args) {        test1();        test2();        test3();    }    //solution    public static boolean verifyArrayIsBST(int[] sequence) {        // 输入的数组不能为空，并且有数据        if (sequence == null || sequence.length <= 0) {            return false;        }        // 有数据，就调用辅助方法        return verifyArrayIsBST(sequence, 0, sequence.length - 1);    }    private static boolean verifyArrayIsBST(int[] sequence,int start,int end){        if (start >= end) {            return true;        }        // 从左向右找第一个不大于根结点（sequence[end]）的元素的位置        int index = start;        while (index < end - 1 && sequence[index] < sequence[end]) {            index++;        }        //搜索右子树的结点大于根节点        int right = index;        while (right < end - 1 && sequence[right] > sequence[end]) {            right++;        }        if (right != end - 1) {            return false;        }        //递归,判断左右子树是不是BST        return verifyArrayIsBST(sequence, start, index - 1) && verifyArrayIsBST(sequence, index, end - 1);    }    /*=======================测试用例===============*/    private static void test1() {        int[] sequence = {5,7,6,9,11,10,8};        boolean result = verifyArrayIsBST(sequence);        if (result) {            System.out.println("YES!");        }else {            System.out.println("NO!");        }    }    private static void test2() {        int[] sequence = {7,4,6,5};        boolean result = verifyArrayIsBST(sequence);        if (result) {            System.out.println("YES!");        }else {            System.out.println("NO!");        }    }    private static void test3() {        int[] data2 = {4, 6, 7, 5};        System.out.println("true: " + verifyArrayIsBST(data2));    }}

---

有不妥当之处,麻烦告知:D