剑指offer：二叉搜索树的后序遍历序列

补充知识：二叉搜索树是指父亲节点大于左子树中的全部节点，但是小于右子树中的全部节点的树；后序遍历是指按照 “左子树-右子树-根节点” 的顺序遍历

low和high分别对应数组得第一个元素和最后一个元素，同样也定义个start=low，因为start要往前遍历整个数组，if (sequence[i] <= sequence[high] )返回false，因为右子树是大于根结点的，然后把数组分成左子树、右子树、根三部分，最后 return VerifySquenceOfBSTCore(sequence, 0, sequence.size() - 1)，判断满不满足！！！

class Solution {
  public:
    bool VerifySquenceOfBSTCore(vector<int>& sequence, int low, int high) {
        if (low >= high) return true;//左子树大于根节点，真
        int start = low;
        while (start < high && sequence[start] < sequence[high]) ++start;
        for (int i = start; i < high; ++i) 
            if (sequence[i] <= sequence[high] ) return false;
            return VerifySquenceOfBSTCore(sequence, low, start - 1) &&
                   VerifySquenceOfBSTCore(sequence, start,  high-1);
        
    }
    bool VerifySquenceOfBST(vector<int> sequence) {
        if (sequence.empty()) return false;
        if (sequence.size() == 1)  return true;

        return VerifySquenceOfBSTCore(sequence, 0, sequence.size() - 1);
    }


};