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BinarySearchTreeIterator.cpp
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BinarySearchTreeIterator.cpp
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/*
Binary Search Tree Iterator
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.
From <https://leetcode.com/explore/interview/card/amazon/81/design/895/>
*/
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class BSTIterator {
public:
//Stack for all nodes in increasing order always
stack<TreeNode *> myStack;
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() {
auto temp = myStack.top();
myStack.pop();
//Remember to call this here
pushAll(temp->right);
return temp->val;
}
void pushAll(TreeNode *root) {
//Push all the leftmost nodes from the root the first time and after each next(), push the right nodes left nodes.
while(root != NULL) {
myStack.push(root);
root = root->left;
}
}
};
/**
* Your BSTIterator will be called like this:
* BSTIterator i = BSTIterator(root);
* while (i.hasNext()) cout << i.next();
*/