二叉搜索树的后序遍历序列

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。

public class Solution {
    public boolean VerifySquenceOfBST(int [] sequence) {
        if (sequence == null || sequence.length == 0) return false;
        if (sequence.length == 1) return true;
        return helper(sequence, 0, sequence.length - 1);
    }
    public boolean helper(int[] seq, int start, int end) {
        if (start >= end) return true;
        int root = seq[end];
        int mid = 0;
        int i = end - 1;
        for (; i >= 0; i--) {
            if (seq[i] < root) break; 
        }
        mid = i;
        for (i = mid; i >= 0; i--) {
            if (seq[i] > root) {
                return false;
            }
        } 
        return helper(seq, start, mid) && helper(seq, mid + 1, end - 1);
    }
}