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.
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class BSTIterator { private: TreeNode *current = NULL; stack<TreeNode*> s; public: BSTIterator(TreeNode *root) { // initialize the current pointer current = root; } /** @return whether we have a next smallest number */ bool hasNext() { while(current){ s.push(current); current = current->left; } return !s.empty(); } /** @return the next smallest number */ int next() { TreeNode* node = s.top(); s.pop(); current = node->right; return node->val; } };
Binary Search Tree Iterator leetcode
原文：http://www.cnblogs.com/sdlwlxf/p/5167679.html