剑指Offer

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。

解题思路

首先找到树的根结点，然后找出比根结点小的和比根结点大的元素范围，若符合要求，则分别是根结点的左右子树，然后继续递归判断。

实现

public class Solution { public boolean VerifySquenceOfBST(int [] sequence) { if (sequence == null || sequence.length <= 0) return true; return VerifySquenceOfBSTRecursion(sequence, 0 ,sequence.length - 1); } private boolean VerifySquenceOfBSTRecursion(int[] sequence, int start, int end) { if (start>=end) return true; int root = sequence[end]; int endLeft = start - 1; boolean isInLeft = true; for(int i = start; i < end; i++){ if (sequence[i] < root && isInLeft){ endLeft = i; }else if (sequence[i] < root && !isInLeft) return false; else if (sequence[i] > root) isInLeft = false; } return VerifySquenceOfBSTRecursion(sequence, start, endLeft) && VerifySquenceOfBSTRecursion(sequence, endLeft + 1, end - 1); } }