173. 二叉搜索树迭代器

173. 二叉搜索树迭代器

题目链接：173. 二叉搜索树迭代器

代码如下：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class BSTIterator {
private:
    vector<TreeNode*> m_stack;//存储节点的数组
    vector<TreeNode*>::iterator it;//vector迭代器

    //递归中序遍历得到的是一个有序序列
    void inOrder(TreeNode* root,vector<TreeNode*>& stack)
    {
        if(root==nullptr)
            return;
        
        inOrder(root->left,stack);
        stack.push_back(root);
        inOrder(root->right,stack);
    }

public:
    ~BSTIterator(){
        //我们在开始时插入了一个不存在的点，析构时手动释放掉
        if(m_stack.size()>0)
        {   
            delete m_stack[0];
            m_stack.clear();
        }
    }

    BSTIterator(TreeNode* root) {
        m_stack.push_back(new TreeNode(INT32_MAX));
        inOrder(root,m_stack);
        it=m_stack.begin();
    }
    
    int next() {
        //先自增，再取值
        if(++it!=m_stack.end())
            return (*it)->val;
        return -1;
    }
    
    bool hasNext() {
        if((it+1)==m_stack.end())
            return false;
        return true;
    }
};

/**
 * Your BSTIterator object will be instantiated and called as such:
 * BSTIterator* obj = new BSTIterator(root);
 * int param_1 = obj->next();
 * bool param_2 = obj->hasNext();
 */
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