【Binary Search Tree Iterator 】cpp

题目：

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.

Calling next() will return the next smallest number in the BST.

Note: next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree.

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

代码：

/**

 * Definition for binary tree

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class BSTIterator {

private:

    vector<TreeNode*> list;

    int index;

public:

    BSTIterator(TreeNode *root) {

        BSTIterator::treeToList(root, this->list);

        this->index = ;

    }

    static void treeToList(TreeNode* root, vector<TreeNode*>& ret)

    {

        if ( !root ) return;

        BSTIterator::treeToList(root->left, ret);

        ret.push_back(root);

        BSTIterator::treeToList(root->right, ret);

    }

    /** @return whether we have a next smallest number */

    bool hasNext() {

        return index < this->list.size();

    }

    /** @return the next smallest number */

    int next() {

        return list[index++]->val;

    }

};

/**

 * Your BSTIterator will be called like this:

 * BSTIterator i = BSTIterator(root);

 * while (i.hasNext()) cout << i.next();

 */

tips：

这个题目的核心就是在于中序遍历把BST转化成vector，这样可以实现题目的要求。

巴特西

【Binary Search Tree Iterator 】cpp

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