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Binary Search Tree Iterator.cpp
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Binary Search Tree Iterator.cpp
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// 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.
// Don't push all into a queue. Take advantage of the feature of inorder traversal
// for each parent node, you look the left most child node
//Can't use BSTIterator as recusive function. It's a constructor
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class BSTIterator {
stack<TreeNode*> myStack;
public:
BSTIterator(TreeNode *root) {
pushAll(root);
}
/** @return whether we have a next smallest number */
bool hasNext() {
return !myStack.empty();
}
/** @return the next smallest number */
int next() {
TreeNode *cur = myStack.top();
myStack.pop();
pushAll(cur->right);
return cur->val;
}
private:
void pushAll(TreeNode *root) {
while (root) {
myStack.push(root);
root = root->left;
}
}
};
/**
* Your BSTIterator will be called like this:
* BSTIterator i = BSTIterator(root);
* while (i.hasNext()) cout << i.next();
*/