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Binary Search Tree Iterator

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Description

https://leetcode.com/problems/binary-search-tree-iterator/description/

Solution

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/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class BSTIterator {
public:
    BSTIterator(TreeNode *root) {
        this->nodeStack = new stack<TreeNode*>();
        this->current = root;
        while(this->current != NULL) {
            this->nodeStack->push(this->current);
            this->current = this->current->left;
        }
    }

    /** @return whether we have a next smallest number */
    bool hasNext() {
        return !this->nodeStack->empty();
    }

    /** @return the next smallest number */
    int next() {
        this->current = this->nodeStack->top();
        this->nodeStack->pop();
        int ret = this->current->val;
        
        this->current = this->current->right;
        while(this->current != NULL) {
            this->nodeStack->push(this->current);
            this->current = this->current->left;
        }
        return ret;
    }
private:
    TreeNode* current;
    stack<TreeNode*>* nodeStack;
};

/**
 * Your BSTIterator will be called like this:
 * BSTIterator i = BSTIterator(root);
 * while (i.hasNext()) cout << i.next();
 */