剑指Offer：二叉搜索树的后序遍历序列【33】

题目描述

　　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。如果是则输出Yes,否则输出No。假设输入的数组的任意两个数字都互不相同。

题目分析

Java题解

package tree;

import java.util.ArrayList;

public class VerifySquenceOfBST {

    public static boolean VerifySquenceOfBST(int [] sequence) {

        if(sequence.length<=0)

                return false;

       ArrayList<Integer> al = new ArrayList<>();

       for(int s:sequence)

           al.add(s);

       return VerifySquenceOfBSTCore(al);

    }

    public static boolean VerifySquenceOfBSTCore(ArrayList<Integer> sequence) {

        if(sequence.size()<=0)

            return true;

        //取出序列最后一个元素

        int mid = sequence.get(sequence.size()-1);

        //System.out.println(mid);

        ArrayList<Integer> left = new ArrayList<>();

        ArrayList<Integer> right = new ArrayList<>();

        //扫描左子树

        int i = 0;

        for(;i<sequence.size()-1;i++)

        {

            if(sequence.get(i)>mid)

                break;

            left.add(sequence.get(i));

        }

        int j = i;

        //扫描右子树

        for(;j<sequence.size()-1;j++)

        {

            if(sequence.get(j)<mid)

                return false;

            right.add(sequence.get(j));

        }

        //判断左子树

        boolean le = true;

        le = VerifySquenceOfBSTCore(left);

        boolean ri = true;

        ri = VerifySquenceOfBSTCore(right);
　　　　　//判断左右子树是否均满足

        return le&&ri;

    }

    public static void main(String[] args) {

        int[] arr ={5,7,6,9,11,10,8};

        System.out.println(VerifySquenceOfBST(arr));

    }

}